Husband sometimes can’t orgasm

I’m 41f married to 42m and we’ve been together over 20 years.

We have a great sex life for the most part. Occasionally he has issues where he either can’t keep his erection or he just can’t cum. When I say occasionally, I mean maybe once every 3-6 months or so. It’s not often enough that it should be a problem….but it kind of is because it makes me feel like complete shit.

I really, really love sex. I’m hot as hell. Nothing knocks me down harder than when I’m feeling like a sex goddess and he’s not into it. He says he is and that I’m sexy and blah blah but the proof is in the limp dick.

So anyway, is this a normal thing for men in committed, long term relationships? Is it lack of interest? A health problem? Age? MY age? Or is it a normal thing that happens and I’m overreacting because my feelings are hurt?