I don’t know how to ride him !!!

Hello ladies, I have been with my bf for a really long time and he is my first sexual partner, and I like having sex with him a lot even though he never makes me cum, because he cums very very fast that I can’t enjoy it for more than 2-5 minuets maximum.

His dick is not big and not tiny either, but I’m a curfy fatty girl, And the problem is that I can’t ride his dick !! It keeps slipping out and I can never make him cum while I’m riding him so we always have to change position !! (He really likes me riding him and I feel that he gets very disappointed when I can’t do it). He won’t tell me that he gets disappointed that he can’t get what he wants because he doesn’t wanna hurt me and make me feel insecure and wouldn’t want me to think that I’m not good enough in bed. ( I also didn’t told him that I never cum with him because he already had a surgery in his balls as on of the balls got hurt in accident, which makes him very sensitive and insecure about himself in bed, and it was very hard for him to get through what happened to him, so I don’t want to let him down, that’s why I’m not that open about this in this stage of the relationship).

So how can I ride him better? Is there any exercises? How can I make him last more?

Thnx ladies for being the only friends that I can talk to about my sex life.