cheating baby daddy

My ex boyfriend and i have been discussing reconciling as we have a1 year old baby together. He recently came to visit for her 1st bday. we ended up sleeping together throughout the week. We started making plsns to get back together he then told me he was seeing someone but was nothinserious and she also had a baby about the same ageas our daughter. I was immediately upset by this as i did not know about her and that he was choosing to raise another bsby but not his own. I asked him to contact her and tell her her plans he refused saying he wanted to do it face to face. He flew home and apparently told her he slept with me. She said she wasn't happy but understood why we slept together and that he was a good person under it all....my ex has told me he has cheatedon all his girlfriends except me However slept with someone after breaking up with me for a week. Should itry and speak to the new gf? I don't believ hes been honest with her. He left when baby was 6 weeks old