My boyfriend is very bad at sex

So me and my boyfriend have been sexually active for about 3 years and I don’t know if it has always been this bad or I just started to become aware of how bad it is. He is my first and only partner and we are going to get married eventually and I’m worried about having bad sex for the rest of my life. How do I talk to him about this without hurting his feelings because sex is a very big part of my life and I can’t live like this forever. I’m just worried because he is very sensitive.