My other half

This is a first time writing a post on here I don't really know what to do I've been with my boyfriend for about 10 months we live together and have everything for baby of which im now 24 weeks pregnant with this morning I understand that I shouldn't have a Facebook password and I didn't actually even know that it was signed in on my phone but he's been speaking to some girl you didn't know that we were together and we sending him pictures of her own underwear and he said she sexy and he's been saying he's going to the shop and actually it's so he can to ring her he talks to a lot of girls and says I have nothing to worry about he want me and the baby but I don't see how some one could flirt with some one else or even need to lie about it if they was happy with you I just don't no how to feel or what to do I feel like it must be my folt I've done something wrong but I try really had I've spent the last 2 weeks taking his mate to work for no money nothing because he asked getting up at 7 30 dropping him off to a different mate then getting home at 1 am I just don't no how to feel it's not the first time he's spoken to some one else and I said okay maybe I'm over reacting but I just want another option