Can a man ever change from womanizer to being faithful to one woman?

I'm talking to a man since one year every day. He is married also lives separated from his wife with whom he has 3 sons. He has three more children, one was born before he got married, one is basically the same age as one of his sons and one is just one year old. The guy is 42, like me, and claims that he is ready for a change in his life. For the last months I have been trying to convince him, that it would be his best interest to try and make things work with the girl ( 24 years old) who has his baby. However, she wants to move on, she has a new boyfriend and my friend feels that apart from their child, there is no connection. I'm kind of wary, I like him very much, but I don't believe that it's so easy to change your behavior. He has been ******* around all of his life so that's clearly what he wants to do and maybe what he knows best. So far there hasn't been any physical contact, we're friends but it's clear that we both want more. He admits to the life he's been living but he says that he is ready for a change and he want me to give him a try. Should I or should I keep things the way they are?