Boyfriend broke up with me

So my boyfriend broke up with me and I slept with someone, now we are back together and he is mad because I slept with someone, he is saying that he feels like the spark isn’t there anymore and all he can think about is me sleeping with someone else

I love this guy so much, I really thought we were done or I would’ve never did,

What can I do to make things better for out relationship I really want it to work he’s my everything