Falling Apart

I am a newlywed. We were just married in June of 2012. Shortly after things starting becoming very distant, he was angry I was angry and we had just lost all communication. I asked my husband if we could try couples counseling and he said it wasn't something he thought he would want to pay for.. Just yet. We kept fighting and were really moving backwards. Then in September I was diagnosed with aggressive stage 2 cervical cancer. This sort of put things on the back burner. I beat cancer just 4 short months later and we were starting to get better. I knew we still had things to work on but I thought maybe the trauma of the situation brought us together. Not long after that we found out we had somehow managed to conceive a baby during chemo. The baby was very sick and we realized we were going to have to terminate. I was 12 weeks at this point. This again, brought us so much closer. And we were during very well.
Then about a week ago I came across a strange email that let to a whirlwind of singles/casual sex/ Craigslist casual encounters/etc. website that my husband had bee posting on for months. Responding to other posts. Emailing to meet up with random women and also initiating more with girls he already knew. Sending pictures of himself, ALL of himself to everyone. When I confronted him about it he said he was going through a hard time. I kept catching him in more lies but he's till swear he's never physically cheated. I'm heartbroken, and scared. He was meeting up with one particular girl the night I lost my hair from my first chemo treatment!! But didn't cheat?! I just.... I'm lost... And shattered. And I don't know what to do.