Cheating Partner Advice

I found out while I was 7 months pregnant that my partner was cheating on me. He had another “girlfriend” while we’re together. It lasted for a year and a half. She was his ex for 4-5 years? The “ex” insisted to be his sidechick. He gave me a lot of explanations but it doesn’t make sense. I gave him a chance because I want my daughter to have a complete family. Now my baby is almost 8 months and I still can’t forget what he did. Any advice? #advicepls