I think my bf is cheating.

So my bf stayed up till 3am sunday night. We had got into a argument cause I eanted him to cuddle with me but He would rather stay up all night and play his clas of clans game on his phone. Last night we got Into it again because he doesn't make me feel important anymore. He didn't come to bed last night at all. He was up all night he didn't go to bed till 9am this morning. I noticed he and a ex of his are now frienda again on facebook. I saw comments between them her sating they should run awat together and him telling her she's sexy. I got upset and co fronted him about it. He says I'm tripping over nothing and its all a big joke. He even told her I was upset and she turned around and said I was nosey. But now they are keeping their talks in private messages. I told him if he wants her then he can go on and be with her and to stop plahing games with me. He swears he doesn't want her. But he knows it upsets me that he even talks to her. We had this same problem about a month ago. They stopped talking and now they started up again. I don't feel that either of them respect me at all. Hes treated me so different since I miscarried a couple weeks ago. We've been trying again. But now its making me wonder if I should even continue to try.