How can I work through my irrational fear of my partner dying?

My partner is in his early 30s and in relatively good health except for the tendency for hypertension and high cholesterol he inherited from his father (who’s still alive and working full time in his 70s). I worry and get upset with him when he doesn’t watch his diet or take his cholesterol supplements because I want him to be around for a long time.

We simply adore each other and have an incredibly happy, loving, and drama free relationship—something I’ve always wanted especially after being in a couple of tumultuous and abusive relationships in my early 20s. I’ve never been so happy in my life and I think it terrifies me a little because losing him would be devastating, especially after losing my own mother to cancer nearly three years go.

I’m not talking about a breakup, which would suck but only happen for a good reason. (As long as things stay healthy between us, I don’t foresee that happening.) I’m terrified of him dying. If I read a story or see a show or movie where someone’s young significant other dying, I will cry and become terribly sad and worried. To lose this man would be to lose a part of myself and I think about what would happen if he were to be killed suddenly in an accident or have a health issue sneak up on him.

Last month he saw a dermatologist because I begged him to after he told me he’d had precancerous moles removed in the past and he hadn’t been in a couple of years. I begged him to the point of tears and my friends who I told about it thought I was crazy. but this is a legitimate fear that I have although I would never directly tell him.

I don’t want to be helicopter girlfriend and thankfully he doesn’t see my concern as a negative thing but I hate how these thoughts make me feel. If he even jokes about dying, I get upset with him and will start to choke up right in front of him.

Logically, I know that the odds of him going anytime soon are slim but knowing that it can and does happen to young lovers sometimes makes me feel a type of anxiety and powerlessness and definitely plays into my fear of abandonment. I’m afraid I would never be able to move on and that dating again would be a useless venture because I’d be able to love someone as much as I do him.

As a coping mechanism, I try to let these feelings be a reminder that I’m lucky to love and be loved this way and that doing such is a risk. We hope to be together forever and while we don’t plan for wedding bells in the near future, we’ve made it clear that we hope to spend our lives together. He makes me wish we could live forever.

That’s the other thing, when I think about growing old with him and him dying before me, I also get so sad it’s crippling for several minutes at a time. I recently saw my grandmother go through the loss of my grandfather after 60+ years of marriage. Although he was sick for a long time, her sadness is palpable I dread potentially going through that with someone I love someday. I’m afraid it would be even worse than losing my mother, which sometimes I can’t believe I was able to cope with at all.

If I’m this insane about a significant other, would having kids make me a nervous wreck? How should I cope with such feelings in a healthy and productive way? Do I brush them aside or face them head on?