I see this as your bf's responsibility. You are choosing not to be involved with his co-dependency issues or his daughter's addiction. I think it is wise to get out. I think many people would want out that weren't tied to addiction by blood or relative.
I don't have much else to add and I don't think it's a bad thing to have some distance. Now if you were married to him you might have the same choices... you choose to not live in this environment. Hugs to you.