HELP!! my BF confessed cheating on me with his baby mama?

[Sam]

so couple hours ago my bf confessed to me he cheated on me with his baby mama. him and his baby mama broke up 5 months ago. we got together 1 month ago. my bf and i live 110 miles away from each other. last weekend i went away for 4 days to boston for work. then we just got together yesterday to hangout and i stayed overnight at his house. This night he just confessed to me that him and his baby mama slept together when i was gone because she told him that she wants him back. he said he was confused so he said he'll think about it and then he told me that he slept with her. he said NOW he knows what he wants and he wants me and he doesnt want to get back with her..he said that he is sorry for what he did. he seems very sincere the way he said sorry..i dont know what to do. i still wanna be with him but im afraid that everytime im not with him he will be cheating on me.. he lost my trust by cheating on me. i dont know what to think. i dont know whats the right thing to do. as of right now i told him i need time to think.. so pls help me!