He can’t stay hard help

My fiance 9 times out of 10 can’t stay hard during intercourse. But he’s always hard when I suck his dick. It’s caused probs in the bedroom because when I’m on top I have to rush to orgasm before he gets too soft and uncomfortable that he makes me get off him. When he’s doing me it’s no better.

I really think he’s like this because he’s use to the tightness of his hand while masturbating, I have reason to believe he also had a porn addiction. And the tightness of my mouth/sucking is the only thing that works for him.

When I try to talk to him about it and suggest he sees a doctor he gets mad/defensive and tells me to not talk about it and says everything’s fine. He also says it’s because he’s tired all the time, but that doesn’t make sense because he stays hard when I suck him.

He’s in his mid 30s.

If you were in my shoes would you want him to go to the doctor now or wait till you are TTC and really need to fix the issue? (We’re not ttc right now)

He also doesn’t have insurance for things like that so I think that’s why he doesn’t want to see a doctor.

Also could this issue even be fixed if I’m right as my reason as to why he’s like this?