Not friends

My boyfriend and I have been together for 4 years we have a 1 year old baby would get sort of along meaning we really don't talk or have many things in common but I do try for us to have a good relationship ... Well after I gave birth to my baby he got a new job and became friends with a coworker who is younger than him by 8 years  his 28. Anyways he started txt her all the time at all times that he they both started flirting with each other I confronted him and the girl and told them to be together but he said he wanted so I forgave him have him a chance and told him not to look for her again... Resently I found he still looks for her and always has I love him but I can't be with someone like that I just don't know what to do cause of my baby