Thank you all.
I do feel that I KNOW the right thing to do, at least for me, is to leave him and give us both space to heal and grow. My problem is that I don't know if I'm entirely sane in thinking so. His family thinks he can do no wrong and he tells me constantly I am selfish. I know I probably sound ridiculous but I do care about him, and he can be a good guy. He's not evil. I do know that even if he quits drinking and smoking that he still won't be perfect, but I do believe that he is much more reliable and considerate when he is not doing those things. I've seen it, and at this point I would be happy with that. I still think space would be good for both of us, but so many people say that when you have children with someone you're supposed to tough it out and not think about yourself. As I said, I know I'm not entirely healthy, and this need to get validation that I have the right to be happy and pursue my own desires even if it isn't what he wants, even if it breaks up our little "family", is part of that unhealthiness. Because I have been in this situation for so long, it has become my reality. I have a hard time separating what is normal/something everyone just deals with, from what is abnormal and should absolutely be changed. If that makes any sense at all.
I really don't want to hurt him, or anyone else. I don't want to become the bad guy, it's true. I don't want his family to be hostile toward me, I still want my son to have his dad and his family in his life. I also have a very intense fear that I will fail again if I try to move on in my life alone. I know, it sounds ridiculous, but again I have been with this man for 10 years, I was only away from my parents for a year or two before we had our son.
I don't say any of this to imply that I am having second thoughts, I had those each time I came back, and then realized it was a mistake to have done so. I have to figure this out on my own but it feels good to be able to write it out. Again, thank you all for the replies.