I need to vent!

So me and my ex recently broke up after almost 5 years. We broke up about a month and a half ago & now he has a new girlfriend. Before I get into everything let me give a back ground. I just turned 20 and he will be 20 soon. We have a son who is a year and a half and a baby on the way. (I am almost 13 weeks). For the last month we have still be having sex, cuddling, good morning kisses before work, ect. But 2 weeks ago that stopped when he got a new girlfriend who is 17. She has no kids and is still in high school. Well Friday while she was at work he called me since we needed to talk about our apartment but after that the conversation turned sexual and lasted for 5 hours. Now today he came and dropped off our son and helped move our son's crib into his room. Well he started talking sexual again and it led to him touching me. I told him no because he was in a relationship & I could only resist so much longer. We ended up in my room and he was kissing my body, he did oral, & we had sex. About an hour after he left to hang out with her. I ain't going to tell her or sabotage anything but damn I am blown away right now.