Setting aside the issues he's clearly bringing to the relationship (and certainly NOT to belittle their importance, especially with regards to safe sex practices), there are a couple of niggling things in my head about this.
First, didn't you break up with him? So why are you drawn back into this if you already ended this a month ago?
Second, it's my understanding that you got involved with this relationship knowing that he was poly and knowing that you could be, but needed to work some stuff out about it. I would suggest that if you intend on getting involved with another poly person, take the time to work that stuff out *before* you get involved instead of while you're involved. It'll probably save you a lot of drama in the long run.
But stick to knowing what your needs are, being very clear about them and recognizing when something isn't working for you.