Katherine Lewis holds the hand of her husband, Dave, who is receiving rehabilitation at a nursing home. (FAMILY PHOTO)

My husband, Dave, may officially be the sick one in our marriage, but his steadily declining health is also doing a real number on my mental and physical well-being. Emotionally, I’m the little silver ball in the pinball machine. I’m alternately angry, resentful and critical; then I’m overwhelmingly guilty, so I careen into being loving, kind and almost a little clingy.

To borrow from the caregiver vernacular, I am the “well spouse.” But “well” is becoming an increasingly relative term.

It’s not much comfort to know that I’m not alone. The Centers for Disease Control and Prevention estimates that almost half of all adults are living with a chronic illness. Assuming most of those individuals have a partner, that’s a lot of really tired caregivers.

Chronic illness is hard to understand if you haven’t lived with it. With a serious illness, the challenge is to beat it and, hopefully, resume your life.

It’s a completely different story when someone is sick all the time; when you lurch from hospitalization to hospitalization, from crisis to crisis. Or when “really sick” is just the status quo.

Terminal illness has an end date. Chronic illness is enduring.

Chronic illness is defined by the CDC as a disease lasting three months or longer. We have that beat by about eight years.

Thirteen years ago, I was in the pediatrician’s office for our baby’s six-week checkup when my cellphone rang. It was Dave. He said he felt a lump on his neck.

The diagnosis came just a few days later: Stage 4 head-and-neck cancer. That was shocking, since Dave had never smoked and was only a social drinker. His prognosis was grim: a 50 percent chance of surviving five years.

Up until then, I had been so happy that the word “happy” didn’t even cover it. After years of longing to get married and have a child, I finally met and married Dave when I was 38; and after more than one doctor assured me I would never get pregnant (“old eggs,” they said), I had Alex at 40.

Finally, I had a life I had dreamed of, and it was even better than I had imagined. I remember thinking: “It doesn’t get any better than this.”

Unfortunately, I was right.

Shortly after the diagnosis, Dave had surgery (a modified radical neck dissection, which involved removing the lump and a lot of muscle and tissue around it, plus a few lymph nodes, since it had spread). After that came grueling, twice-a-day radiation for seven weeks. Recovery from the treatment alone took more than three months.

But eventually we got our miracle: Dave was cured of the cancer, which has never returned. We didn’t know it then, but he would never recover from the damage inflicted by the treatment.

(Although it would be impossible to prove that the twice-a-day radiation caused Dave’s subsequent problems, doctors we talked to in the years that followed always expressed surprise at the protocol. There’s also the fact that the medical center he used no longer uses that protocol, reverting to daily radiation.)

For five years post-radiation, we lived with gratitude and joy. Then, Dave’s poor body began to deteriorate piece by piece. His digestive tract and his lungs were affected the most; and after one too many hospitalizations for aspiration pneumonia, Dave had to get a feeding tube. It’s been seven years since he’s had anything to eat or drink by mouth; it’s all through the tube.

Then a few years ago came the tracheotomy — putting in the disfiguring, voice-garbling apparatus that allows him to breathe.

Now he has an inch-long piece of plastic protruding from his neck. He puts a finger over it to talk — to croak, really. He’s almost impossible to understand.

At 6-1 and 140 pounds, his cheeks are sunken and his shoulders hunched. He looks concave. He is 68 years old.

Alex is now 13 and he loves his dad desperately. But the fact is, he doesn’t have a normal dad. And when you’re a kid, all you want in life is to be normal. It has been nothing short of horrendous for him.

Dave can’t eat, can’t drink, can barely speak and is usually in pain. Yet I’m the one who’s usually complaining (“Could you have possibly folded that basket of laundry while you were watching ‘CSI’?!?”).

But it’s just so hard. I work at a full-time job for the government, and also write and do public speaking (on such subjects as anger and control, not surprisingly). I also take care of Alex, do what passes for housework and visit my 91-year-old parents.

Contrast that to Dave (who was once a very successful engineer), who now watches TV — a lot of TV. In fact, he spends most of his time lying in bed, watching TV; that is, when he’s not lying in bed, reading. Of course, there are also doctors’ visits, physical therapy and, when he can — since he still drives — going to the grocery store for us and sometimes making dinner.

My hunch is that the television is a way to check out. I also know the painkillers make him sleepy, and the pain is lessened when he’s lying down. But I do believe the television is his most powerful drug, allowing him to ignore the reality that is his life.

I know that most of my anger is really about our situation, our lot in life. But you can’t lash out at a situation, so Dave gets the brunt of it. Then comes the guilt, and I beat myself up for being such a witch.

That is, until I come home and find Dave right where I left him: in bed. Watching “Law and Order” reruns. Or the Military Channel (“You don’t have to keep watching that,” I’ll say. “I’ll tell you how it comes out. The Germans lose.”).

I don’t have to be Freud to understand that the anger is really a defense. If I had to actually sit with the feelings — the sadness, the grief, the fear, the longing for how things could have been — I might never get up again. So I’d much rather feel angry than so very, very sad.

Yet as bad as it has gotten for him, Dave has never, ever said he was done with this life. He is an incredible fighter, and I believe that as long as he gets to be with Alex and me every day, he wants to hang on.

I do know the Dave I fell in love with is still in there: generous, thoughtful, loving and totally supportive of me and whatever crazy goal I want to accomplish. And I am completely grateful for the life he gave me: a loving marriage when I thought I would never find the right man; the child I thought I would never have. I came so close to missing it all.

Those thoughts fill my good days. But there are a lot of bad ones.

There is one time each night when I can pretend nothing has changed. When Alex has finally gone to sleep and the dog has, too; when I put my book down and turn out the light, I reach out for Dave, and he reaches back. And he’s still the man I married. And in the dark, when I can’t see anything different, we’re just a normal couple, turning in for the night.

I love you, Dave.

Katherine McQuay Lewis lives in Bethesda.