Can't let go for the right reasons..

My husband and I have been together for 6 1/2 years, we have been together since we were teenagers so we grew up together in a way. We have always been there for each other but he has not been the best partner, he hasn't treated me good in years and he has cheated on me before. He tells me all the time I deserve better and should go be happy. Yes I do deserve better and want to be happy but I can't seem to let go of him. I'm too attached to him. We have those really good moments but then we have the really bad moments. I matured so much more than he has, so it feels like im trying to raise a boy but he's already grown I can't raise a man but I keep holding onto the relationship just waiting.. hoping he'll mature & treat me better. He's my best friend we have always been there for each other. We have a child together and he said if we split up he would only talk to me if it had to do with our son. I don't ever want him out of my life which is why I keep holding on but I'm not holding on for the right reasons.. any advice/guidance?