Can’t believe how stupid i am!!

Need some opinions/advice please

So basically me and the baby dad split up last month, obviously he went straight into another relationship.

So I let him stayed over for Christmas for 2 days to spend time with the baby.

We slept together. He hugged me apologising for everything and hurting me.

Then Boxing Day he said he was ending things with the girl, as he said he rushed into things etc and that he wants to put the baby first. Then asked me if I’m happy about it. 🫠

Well…. Later on the girl who he was ‘dating’ messaged me on Facebook and she told me everything about him and how he cheated on me while I was pregnant.

Obviously I confronted him, he denied it. I’ve give him opportunity to tell me the truth but instead he didn’t. I believe the girl than his lying mouth.