husband has been lying to me?

I caught my husband with pictures in his phone of some girl he works with and all I did was simply ask him why? He replied, "because I was horny and it showed more skin then usual" I feel like complete shit at this point. I asked him to not talk to her anymore and to not do it again. Fast forward to today, he is gone on a short deployment I was texting him about our son having surgery tomorrow he stops but I scroll through facebook and see he is replying to comments she left on one of his pictures but not replying to me. So I found out this entire time he has been lying to me about not talking to her. We have a 4 year old and I'm 7 months pregnant. I have no idea what to do. He said he "doesn't like to be told who to talk too" but just the pure fact they're talking KNOWING what he did to her pictures makes me feel like shit and sick to my stomach. I have no idea what I did to deserve this...