My husband, Rob Kelly, is a retired N.F.L. player. After five seasons as a safety beginning in the late 1990s, four with the New Orleans Saints and one with the New England Patriots, he sustained an injury to a nerve between his neck and shoulder during training camp that ended his career. By the time he retired in 2002 at 28, he had been playing tackle football for about two decades.

Rob had no idea, however, that all those years of playing would have such serious consequences. Safeties are the last line of defense and among the hardest hitters in the game. One tackle he attempted while playing for the Saints was so damaging, he doesn’t remember the rest of the game. He got up, ran off the field and tried to go back in — as an offensive player. He knows this only because people told him the next day.

Professional football is a brutal sport, he knew that. But he loved it anyway. And he accepted the risks of bruises and broken bones. What he didn’t know was that along with a battered body can come a battered mind.

For decades, it was not well understood that football can permanently harm the brain. Otherwise, many parents would most likely not have signed their boys up to play. But this reality was obscured by the N.F.L.’s top medical experts, who for years had denied any link between the sport and long-term degenerative brain diseases like chronic traumatic encephalopathy.

That started to change in late 2009 when, for the first time, the N.F.L. publicly acknowledged that concussions can have long-term effects. In 2016, a top league official admitted that there is a connection between football and C.T.E., which has now been found in the brains of more than 100 deceased players. But for Rob, and countless other players, those admissions came too late.

When I first met him in 2007, Rob had this gentle, endearing way about him that caught me off guard. I had never watched a full game of football in my life, but still believed the stereotypes: Players were tough and abrasive. He was neither. I had never met a man who was so sensitive and tenderhearted. I loved that he wasn’t afraid to be vulnerable and to show tears.

When we married in 2009, I already knew he was an amazing father. He could play dollhouse with my stepdaughter for hours without a hint of boredom. This continued when we had two children of our own. When our son was born and I was focused on taking care of a baby, he would bathe the girls, brush and blow-dry their (tangled!) hair, then put them to bed. Afterward he would wash the dishes. He brought me coffee in bed each morning. I was spoiled rotten.

But since I had known him, he had trouble sleeping, and he has been prone to mood swings and depression. In 2010, things got worrisome, so I arranged for him to be evaluated by neurologists so that he could apply for disability benefits. We traveled from Ohio, where we were living at the time, to North Carolina for full cognitive evaluations and testing. There were seemingly endless amounts of paperwork and record keeping.

I was right to be concerned.

Over time, I had started to notice changes. But this was different and, around 2013, things had become much more frightening.

He lost weight. It seemed like one day, out of the blue, he stopped being hungry. And often he would forget to eat. I’d find full bowls of cereal left around the house, on bookshelves or the fireplace mantel. The more friends and family commented on his gaunt frame, the more panicked I became. By 2016, he had shrunk to 157 pounds. That’s right, my 6-foot-2 football-player husband weighed 157 pounds (down from around 200 when he was in the N.F.L.). People were visibly shocked when we told them he had played the game professionally.

Besides damage resulting from football-related concussions, my husband has never had a diagnosed brain injury. He’s never been in a car accident or fallen off a roof. He never took steroids. After struggling in retirement with alcohol abuse for about six years, off and on, he hasn’t had a drink in eight years. And he’s only 43.

When you live with someone with brain damage, you become highly attuned to your environment and develop an intimate relationship with your senses and intuition. Your hearing becomes excellent, almost unbearably keen, like a movie character who develops supernatural abilities overnight. Rob’s mood swings scare me sometimes, and I always have to be in tune with early signs of his agitation. I try to protect him from stress so he won’t be overwhelmed. It’s exhausting.

Our fights went in bizarre circles and were never resolved. He would be irrationally upset about one thing but would quickly lose track and begin rambling about something that had no connection to the topic at hand. Every argument we had ended with me thinking: “This isn’t normal. This is not what couples fight about. Something’s wrong.”

And the arguments were always the same. It was as if our lives were on a loop, like some song that’s been left on repeat for years. That sort of repetition has a tremendous ability to make you feel like you’re going insane. And maybe, you wonder, you are.

He was losing touch with reality and was getting more and more paranoid. The first time he accused me of stealing loose change from his nightstand I was speechless. And when I told him how illogical it would be for me to do such a thing, he looked at me with even more suspicion. But his paranoia didn’t end there. It would leave me with a heaviness in my chest that made me sob without warning.

He went from being a devoted and loving father and husband to someone who felt like a ghost in our home. For a couple of months one winter he was so depressed and detached, he couldn’t muster up the energy to speak. My questions went unanswered until I simply stopped asking them. The silence was unnerving.

So we were relieved when, in January 2013, we were told that the Bert Bell/Pete Rozelle N.F.L. player retirement plan and supplemental disability plan had awarded him total and permanent disability benefits. His benefits were listed as “degenerative,” which establishes that his “disability arises out of league football activities” and had manifested within 15 years of his last season. He is entitled to monthly payments for the rest of his life. (These payments are separate from the estimated $1 billion settlement of concussion-related lawsuits with thousands of retired players, for which we have registered.)

The examining clinician found that “repeated concussion is very likely to have caused Mr. Kelly’s neuropsychological dysfunction,” and also that his prior alcohol abuse may have been a factor. But he has not had a single drop of alcohol for eight years, and his condition continues to deteriorate.

After years of little to no sleep, he alternated between sleeping either three hours a night or 20. I’d wake up to find every blind and curtain in the house closed and Rob sitting on the sofa with a blank expression on his face. He no longer felt comfortable driving, refused to leave the house and cut off contact with everyone.

Specific details about how he wanted his funeral to be, and his demand that he be cremated, were brought up with excruciating frequency. One particularly dark time, he went five days without eating anything; he drank only water and a few swigs of chocolate milk. He was suffering deeply and barely surviving. My love and affection seemed to offer no comfort or solace. I felt helpless.

It wasn’t until I joined a private Facebook group of more than 2,400 women, all connected in some way to current or former N.F.L. players, that I realized I wasn’t alone.

Our stories are eerily similar, our loved ones’ symptoms almost identical: the bizarre behavior I had tried to ignore, the obsessive laundering of old clothes — our washing machine ran from morning till night.

It was comforting and terrifying all at the same time. Why did so many of us see the same strange behaviors? “Our neurologist said they do it to calm their brains,” one friend told me.

Symptoms consistent with C.T.E. are a recurring topic in the Facebook group. They include memory loss, confusion, impaired judgment, aggression, depression and anxiety. These problems become apparent sometimes years or even decades after a player hangs up his helmet.

One woman may write a post, desperate and afraid of the man her husband is becoming — the rage, mood swings, depression, memory loss. A man so drastically different from the one she once knew. Hundreds of comments will follow, woman after woman confirming that she is going through the exact same thing.

While the symptoms and behaviors are telling, C.T.E. can be conclusively diagnosed only posthumously, because it requires the close examination of brain tissue. But many of us, including me, are convinced our husbands suffer from the disease. We try to comfort one another with the same words: “Just know you’re not alone.”

I don’t think the public has any idea how widespread this problem truly is. Rob and I hope that, in telling our story, we might help other families. There are likely to be hundreds of wives and partners of football players, maybe more, who live a life like mine. Sadly, there is a feeling of shame among those affected, in both the men and their families.

But who these men have become is not who they are, and I write that with conviction. The symptoms they display are beyond their control and occur through no fault of their own. These men chose football, but they didn’t choose brain damage.

I used to read all the articles about C.T.E., all the stories about football players committing suicide. I’d skim the comments to see remarks like: “They know what they signed up for” and “Of course football is bad for the brain, everyone knows that.”

But when all those big hits happened and the fans cheered, did they cheer despite knowing a man just greatly increased his risk for dementia? Was anyone worried about an A.L.S. diagnosis or a C.T.E.-related suicide at 40 after their favorite player suffered repeated blows to the head on the field? No, they cheered and they celebrated because they didn’t know. And neither did we.