My boyfriend can finish from oral but not sex

My boyfriend can’t finish during sex. I’m not sure what to do about it. He can finish from everything else but just not that. We’ve talked about it and I really don’t think he has anxiety about the relationship (he talks about getting married and proposing all the time). He’s also cut out porn and masterbation and it hasn’t helped. We have the thinnest condoms you can buy. I don’t know what to do at this point. I love him but I don’t know how to help him. I can’t help thinking about having kids or what would happen on our wedding night if we were still having these issues. He really doesn’t want to talk to a doctor but we’ve been having this problem for over a year. I’m scared if I keep pushing the topic he’ll have more anxiety about it and the problem will get worse. I would really appreciate any advice or words from anyone who has had similar problems!!! Help!!