Eek, well it seems that sex is tied up with the rest of the relationship. Not that it shouldn't be, but it seems like it's about half of your paragraph.
So, first, the sex. Premature ejaculation happens. One thing you can try (assuming you may want to salvage things) is to get him to see his doc and make sure it's nothing organic. Assuming it's not, there is going ahead in one way (oral sex, etc.) for his orgasm #1 and then going to the main event. Second time is generally going to be slower than the first.
You're right that there are going to be some positions where he gets off faster than others. The time to talk to him about that is certainly not during mid-thrust -- it's not right before and it's not right afterwards, either. You've gotta pick your moment and not make it tied up too intimately with the act. So, it's Friday afternoon and you've both just had lunch and you're at home -- might be a time to talk.
And for God's sake, instead of framing it as a negative (because this guy is a bit concerned about his performance anyway so framing it negatively is only gonna fuel that), frame it as a positive. E. g. honey, y'know what I really like? I like it when we do cowgirl position
(or whatever it is you prefer). Here, lemme show you.
And then do it.
This will frame it as a positive.
You are not only fulfilling your own needs but you are also giving this guy a shot at success.
But this is all assuming you want to salvage the relationship. Do you? That's the ultimate question. The rest of it is window dressing.