Husband found someone else

My relationship with my husband has been on the rocks for a few months now. He has stopped coming home after work every night, and only come home one day a week when he is off work to see iur daughter. He will then usually leave when I put her to bed. Ive been trying to figure out what is going on, and so today I finally confronted him. I asked him why he doesn't want to be home anymore, but all he could say was he is stressed out, and doesn't want this baby, I'm pregnant with our second which wasn't planned. I asked him if he still wanted to be with me, and he said he didn't know. I then asked him if there was someone else, and he said maybe. I asked him who it was and he told me that it's his coworker, assistant manager. He's been staying at her house. I asked if he had kissed her, and he said yes. I asked if he slept in the same bed as her, and he said yes. I asked if they've had sex and, he said no. I don't know if I believe him. This has been going on at least since June, which I only know because he changed his password on his phone. He didn't even want to tell me when it all started so it could have been going on even longer. I am devastated. This girl is 5 or 6 years younger than me, she knows my husband and I have a daughter together and are pregnant with out second. He has chosen to build a relationship with this girl instead of coming home every night to try and repair ours. I do everything for him, and I dont know what I did to make him do this to me. I am beyond devastated. I love him with my whole heart, and I feel like I've wasted 9 years of my life building what I thought would be our forever. I have packed enough stuff to stay at my parents house for at least 2 weeks. I will then come back and get the rest of my stuff I guess and see where to go from here. He's been doing this and still kissing me, while kissing her. He told me I don't deserve this and he's confused and feels like shit about the whole situation. I don't even know if I believe that. I'm so lost right now and heart broken.