He never cums during sex, and it makes me feel self-conscious.

So, this guy and I have been sleeping together for a decent amount of time now. It's weird though, because he never cums. He's even gone soft during sex before, and a lot of times he has a difficult time getting it up when we're about to get it on. (Word play intended. 😂) I can simply accidentally rub against him and he'll get hard. Sometimes he can even look at me and get hard. It makes really self conscious that he can't when it comes to us having sex though. Plus, he can cum if he jerks off himself, but with me he never does. It just makes me feel really self-conscious. I don't know how to approach it. It kind of makes me not even want it anymore, because it makes me feel really bad. He says it's not me, but I feel like it is. We're not even 20 yet, so it's not an age thing. I just can't help but think with other girls he probably has, but I'm just not good enough. He's the only guy I've ever slept with, so I don't know. It just really bothers me.