Fizzling sex life

My boyfriend and I have been together for a while now, and even though we have sex like every other day, I feel like he isn’t as satisfied anymore. He takes forever to cum, which has always been a thing unless he masturbates, but I’ve been noticing that sometimes it’s hard for him to even keep his boner. I feel like I’m doing something wrong and it makes me insecure because he’s cheated in the past, and I don’t want him to go find satisfaction with someone else. Does anyone have any tips/ideas to try to revamp your sex life?