it's because he's (obviously) immature and lacks any form of self control, which repels women like nothing else.
Actualy that is often very untrue. There is a large number of women attracted to "bad boys" who often lack self control. In fact quick to be violent against those who offend them is often a trait of such bad boys.
People that hold extreme grudges and get revenge on those that they feel did something wrong. Traits such women can think is attractive or sexy until it turns on them.
Then those women one day realize all those horrible things they did to people that upset them might not be so attractive after all because they are suddenly the one upsetting them.
They also realize those same tough guys often have spent a lot of time in trouble with the law, and are not so detered by it anymore.
Similar problems can happen in reverse. There is a number of guys that think some woman with a bad girl attitude is attractive. You see the same thing in movies and on TV marketed as a form of sex appeal. They then are surprised when that same attitude causes them a lot of relationship drama and problems later in real life.
Back to to the topic at hand. She can either takes steps mentioned by many here if she feels her safety requires it, cutting off all contact and getting a restraining order, or she can try and get some of the property.
She was not married to him though and in all honesty is not entitled to any of the man's property, especialy the equity of a home, often the most valuable property a person owns.
If she does get a restraining order the man would be within his rights to have the Sheriff serve her with an eviction notice. I don't know the eviction laws of your state, but she won't be getting a dime from a home that does not belong to her in that case, and will need a new place to live in short order.
Further restraining orders often work both ways, and lose all merit if she breaks them. That means she will need to communicate with him through a third party and contact his lawyer as well.
Most lawyers will also advise anyone with a restraining order filed against them to also file one. I have seen civil cases between others where that was pretty much standard and both entire families had restraining orders against another entire family and would renew various temporary ones constantly for years at a time (until the other side finaly lost after both had spent six digit sums in court over a couple years.)
I think it would be pretty foolish for anyone with a restraining order filed against them to allow the person it protects to live on thier property. Would be kinda hard to be a landlord or inspect your legal property if you can't go near them or thier residence. If a renter filed a restraining order against me an eviction notice would immediately be delivered by a third party such as the Sheriff. Anything else would be foolish. Be hard to collect rent, inspect property or do all the jobs, some even state required that a landlord must do. That is just basic logic, regardless of any other facts, past relationship of some sort or not. It would be foolish involving any renter to let them stay.
So if the guy has half a brain I would expect the same from him, nevermind that he is a former lover with even more emotional reasons to be vindictive.