The only boundary I feel I could set right now is to tell him to get out. As Sandi says, don't set a boundary that you are unwilling to enforce. And I'm not so sure I'm willing to enforce that.
Now, with that said, I am also unwilling to let him in my bed (although he's not said he wanted to come back). I am unwilling to be affectionate (he's tried that a couple of times). I am unwilling to sit in the living room hanging out with him as if everything is great. I need my own space and my own time and I've told him that. But the more I try to tell him that, the more he's knocking down my door. So there's not much else left other than to throw him out, I don't think. Please tell me if you don't see it that way because I'm so close to the situation maybe I've got it all wrong and there's some other boundary that I should be placing.