Single and pregnant

So me and my boyfriend are expecting a baby I am currently 9 weeks and 6 days!! We've been arguing a lot and we have split up a few times, we both love eachother but it's just not working at all...the other night he said something to me that I can't get out of my head...he said he had shagged someone else but then said he hadn't and said it to see if I would say it back, I thought is this some kind of sick joke?? I certainly have never cheated but he clearly doesn't trust me and I sure as hell cannot trust him now after that...a certain girl everytime we split up he adds back onto his Facebook like he knows she gets to me but I'm getting bored of that now...I don't understand him and what he's achieving from this? He would rather let his gf and unborn child walk out of his life than work things out I'm questioning if he ever loved me?? I can't understand why I would want him back either as he lied to me about cheating on me which is not a normal thing to do :(