and this exgf of his, was with him before you got pregnant or
between the time you got pregnant or?
One possibility could be that he is guilty, upset with regard to
his ex-gf. He doesn't know how to handle her, and possibly he feel
that if not for you (your existence, not your actions), she would
not become this problemetic. It doesn't mean he still misses her,
but guilt can be talking.
On the other hand, perhaps he is remaining with you for the same
reason that he feels guilty towards you. However, his resentment is
growing because though he initiated a rship cos of guilt, maybe he
just isn't ready. I'm speculating of course.
I think your rship carry too much unresolved emotional baggage for
two young people to keep on with it. And with things like emotional
baggage, you can't just open it like a can of worms and expect a
peaceable, acceptable solution to 2 (or more) people.
In a situation like this, there isn't much of a point confronting
and 'forcing' a solution because the time isn't right. There's
nothing to prove who's right, who's wrong, except that right now,
the journey is stormy with each other. Perhaps what you need to do,
is a bit of 'travelling' on your own and hope that when you put
some space and time between you and him, the emotional baggage will
be lost in transit, and you can start out anew IF you want to start
out anew.