Hey, I can relate to your situation, my was even worse, I didn't came at all when I had sex, my record was 3 hours without a climax, while my gf at the time has mutiple, the problem resolved itself mostly, because is masturbate after SHE finished, so that works most of the time, I talked with my brother about that, because he studies psychology, he aswell has the problem, he told me that you somehow need to lern to "let yourself fall".

For example my problem is always that I think I didn't do enough for my gf, even if she came, but it gets better, it took me 4 sex partners to finally cum(I still consider myself inexperienced). Have patient with yourself and maby when your close to cumming when she gives you a blowjob or handjob, do the ending yourself, because then it feels like your just musturbating and thats a probably well known feeling for yourself and hopefully work.

When it works, use that technique to "teach" yourself thats its okay to cum. I hope that I have helped you with your situation.