What to do?

found out i was preg. in july. me an the boi were together before in high school and tried things agin. turned out he was cheating on me all summer i just found this out. he said he did this because he doesnt know who he wants to be with. so we confronted him face to face he denied me and then talked to me a week later and said he was mad cos i told the other girl i was preg. an he wanted to tell her himself. we were ok the past week or so he been callin me seein whats up an stuff. the thing is he put me through allt his stress and im carrying his child. we hung out all year and all summer and that kills me because he was with that girl too. we arent togetehr right now and lat night i told him i cant do this anymore. we basically argue all the time right now. he wanted to hang out over thanksgivin break but come to finmd out he is still chillin with that girl. we have no choice but to atleast be friends but i dont want to be. but ihave to because of our child who is due in march.??help