Relationship advice

I was with my ex for 6 years, he broke up with me because he “needed space” and he then got in a relationship with his old best friends ex gf, they were together for a couple month and he got her pregnant. She is 6 months pregnant & he no longer wants to be with her he is choosing me again. He said he’s willing to show me all the proof of them only contacting eachother regarding their baby. I am willing to give him a try but it makes me upset about his mistakes that he did.

We are now expecting also I am 4 weeks pregnant and I don’t know if I should let him be part of our life or do it alone.

What would you do ? How would you feel?