You can tell him that women and men feel differently about sex-- for him, sex is THE act to show love, but for you, sex is the culmination of loving feelings -- and the fact that it is occasional doesn't bother you.
Tell him you'd rather have him in your life than not, issues or not -- that you are with him because of who he is, not how often you have sex.
Tell him that it's importat to YOU that he stay on the medication, because you want him healthy and that just being with him -- doing anything or nothing is what really makes you happy.
And finally, tell him that there are other ways to be together sexually and achieve orgasm without his penis everytime, and that you are happy with those things just as well.
You are probably not imagining that. You may want to tell him that you aren't feeling "sexy" lately, and you aren't really interested anyway. It might let him off the hook enough to relax...