OP - i’ll try one more time and then i’ll shut up, because you aren’t hearing me.
You may be more experienced than him with sex, but you are still very clueless about it.
And what you are doing is, most likely, making things worse.
Yes - there are a lot of men for who sex is simple and straight forward process - penis goes up, PIV, sex, climax.
And then there are men, who are less confident, for whatever reason. For them - once they experience an issue - which happens to most men at some point of their lives, btw - something goes wonky...
So - the more confident men just shake it of. The less confident men get concerned that this would happen again and worry. And once that worry enters their head, it’s there and it happens again and again.... self fulfilling prophesy
What you are doing - making it a focus of your relationship right now, telling him how important PIV sex is, and that he might need to see a doctor, etc - all of it will, most likely make it worse. Not help him relax.
I think there are insecurities on both sides. His - with his erection and ability to satisfy a woman.
And yours - with equating an erection and his PIV orgasm with your attractiveness....
There is more to sex than piv. Give him a chance to overcome his insecurities as you mention you like him and you click.....
Sex isnt a tool to reinforce self worth, or to prove anything....
And don’t expect him to be responsible for your orgasms....
So - if you want to try to see if it’s fixable - get the piv=only type of worthwhile sex - sort of mentality and try other things..... And give you both a time with no pressure to perform... While exploring your bodies together and building intimacy. There are so many wonderful ways to do that.
Good luck.
PS : this all assumes he doesn’t have a medical issue.
And, for the record - only a doctor can tell him if he needs circumcision for medical reasons...