Me & mii boyfriiend of 3 years?

ME AND MII BOYFRIEND OF 3 YEARS R EXPECTING A SON IN SEPT....AT THIS POINT WE CANT GET ALONE AND HE HAS TOLD ME THAT HE HAS CURRENTLY STILL BEEN MESSIN WIT HIS EX WHICH IS ANOTHER BABYMAMA..UMMMM I REALLY WANNA LEAVE HIM BUT IM STAYIN WIT HIM BECUZ OF THEE BABY BUT AT THIS POINT I DONT WANT HIM NE MORE!!! WHAT SHOULD I DO???