Am I overreacting about this!!!!?

So this year was my first time spending Christmas with my boyfriends family it was going great until his ex showed up with a baby that MIGHT be his....they don’t even know yet if the baby is his, but she clingy to his family I never seen her clingy to the other man family. It’s annoying because I have came to the fact if the baby is his I’ll have to end the relationship because I just can’t appreciate the fact he would have a child and he deserves someone who does. So seeing her and the baby just made thing very awkward for me. I told him if I knew she and the baby was coming I would have waited until tomorrow to come. He told me I was overreacting. But I honestly don’t feel like I’m am. I just wanted to remove my self from a uncomfortable position so I left and went to my cousins house for the remaining of the night.