When sex is really bad

So I’ve been with my boyfriend for almost two years and I love him a lot. I feel like he enjoys sex a lot more than I do when we do it. Sometimes I worry that it will become a bigger issue in the future but I don’t know either. I don’t want to talk to him about it because he’s already insecure about it and I feel like it will just make things worse. I think there was a good period of time when sex was really great and it wasn’t when we first started dating but I think it was when our feelings started getting stronger for each other. We are living together and we have sex I guess a good amount but I feel like I enjoy masturbating more...like a lot more. Maybe it’s just me I feel bad that it’s even a thing and I don’t know what to do.