Ex Boyfriend

My ex and I have a daughter together and we have been apart 2 months but things are so awkward with him. It's hard for him to even bring my name up, he never makes eye contact with me, and it's hard for him to even talk to me. He acts so nervous and uncomfortable when I'm around. On Facebook he claims to have a new girlfriend (His Ex) but keeps it completely hidden from me when I don't know why. He makes it so hard to Co parent when he behaved so awkwardly. One minute he'll talk and we'll have a nice conversation and the next he's back in his shell, he's so hot and cold. Any ideas on why he'll behave this way?