My last relationship messed sex up for me. Any tips to get back too normal?

I was in a 4 year relationship with my ex and throughout that relationship, 90% of the time we’d have sex, it would end with my “jerking” myself off to cum. I didn’t find anything wrong with this because it was what I was used to and therefore since the sex was still good, I didn’t think much of it. We would have sex for 15/20 minutes then I would make myself cum with masturbation. Now that we broke up and I have other sexual partners, I realized that I can’t cum from sex/oral/handjobs. I’ve had better sex with my new partner than my old partner but I’m now just realizing that she can’t make me cum. We’ve had sex 3 times now and I haven’t cummed once. I just go soft and can’t get hard again after 20 minutes of sex.
Any tips to help me cum again?
I’m currently on day 15 of nofap but I did watch porn for like an hour the other day but I didn’t masturbate.(I know I shouldn’t have watched the porn to begin with). I’ve had sex twice between those 15 days and haven’t came. I’m planning on seeing her again in 5 days and I want to make sure it doesn’t happen again.