I really need some advice.im 19 week pregnant and also have a 8 month old baby and my bf walked out on us last weekend.

I had received a message on fb from a lass claiming she was sleeping with my bf so obviously I questioned him about it.he denied it and said it was some bitter lass trying to ruin what we have.obviously it played on my mind and my hormones didn't help and we hardly spoke for a couple of days during the argument I told him to leave cos I didn't wanna be treat that way.and last weekend he did just that packed up and left and I've not seen him since.we have been txting but he is so angry I believed this person over him I don't think he would do that to me deep down buy my hormones player a big part in convincing me it's true now I think we're done for good I'm heartbroken.what should I do