Seems like the most accurate and reliable indicator of how a man will treat you in a relationship can be deduced by how he has treated past girlfriends. If I had to pick between analyzing his relationship with his mother and his ex, I'd choose the ex.
Thessaly is right that his relationship with his mother will inform his interactions with women. But how his maternal dealings influence his SO dealings can be very complicated. For example, his mother may be just plain nutso. And he might display maturity by holding her at arms length. Another son might be raised to be a Mammoni (Italian, for mama's boy) and hasn't had enough life experience to properly individuate himself.
What's most relevant is how he treats his girlfriend who's stuck in the middle of all this.