Sexual frustration

My partner and I tend to not see eye to eye when it comes to sex. He takes a medication that effects his ability to preform and when he looses it or can’t finish it makes me feel super bad like it is my fault so I stop. He gets upset when I stop and doesn’t understand why I feel bad about it. It has been causing a strain on our relationship as a whole and I am not sure what to do. I’ve tried explaining my side to him and he either refuses to understand or just doesn’t understand at all. Any advice?