We broke up, we live together, I want him back. Please help?

Okay, so me and my boyfriend have been together for 4 years we have a son and I'm pregnant with our daughter, I'm 18 and he's 20 we have lived together for the last year anyway things haven't been that good in a while but I've always stayed by his side, I've put up with so much from him.. Like never being home and things like that, I can say I've been very insecure with myself lately and if he would even follow a girl on Instagram I would flip but I found out he was talking to a girl she said just as friends but I read what he said he never once mentioned he had a girlfriend... And he was clearly flirting with her I could tell he likes every picture she puts up and no one else's not even mine just hers, he broke up with me after I confronted him about talking to her he just said he didn't want to be together anymore I don't know what to do we live together but he wants nothing to do with me I'm 9 months pregnant with our second child if there is anything I can do to maybe help I will like, I said he's being very distant, sleeping in the couch not speaking to me. Etc. what can I do to try to get him back?
We broke up, we live together, I want him back. Please help?
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