Boyfriend can’t cum from sex?

Hi all! This is an awkward topic for me but my boyfriend (40) and I have been together for 9 months, have an amazingly happy and healthy relationship, but I notice he seems to struggle to finish when having sex.

In the beginning when we began, I noticed on and off he would go soft during sex, which I equated to being new partners, performance anxiety, and him being insecure about himself (all of which he has opened up about). That problem after a month or two went away and he had no issues finishing - if anything, finished quick! He was still learning my body, so I wasn’t necessarily finishing so he would put a lot of focus on trying to “perform well” for me.

Fast forward to the last 2 months-ish, he seems to struggle to finish almost every time. We could be going for over an hour before we call it quits. He said he thinks it’s because he’s concentrating on making sure I finish also, but even when I do, he still can’t complete. I’ve tried everything- dressed up, foreplay, encouragement, and nothing helps, to I’m starting to feel like he doesn’t find me attractive (which he swears is not it). I’ve asked all the time what he enjoys and what can I do, and he says he already loves what I do! On the flip side, if I use my mouth, he finishes right away!

He says he's not sure why he’s struggling to finish during sex, and says he isn't frustrated by it the way I am. We've been having a lot of open discussion about it. Apparently he has never had this issue in the past, and also doesn't seem to go solo (so not iron grip).

Any advice would be greatly appreciated. I just feel so upset and that maybe I'm just not attractive enough, but I'm doing my best to not show him that or make him feel bad for what he can't control. Help!