Unfortunately, one doesn't have to pick a lock or break a window or door to get convicted of a burglary. You can use a set of keys and be a burglar. All that's required is that you enter the premises without the permission or authority to do so and with the intent to commit a crime inside. (See statute
) This would be a felony of the first degree
in Pennsylvania, which means that he could receive more than 10 years of prison for this offense.
The domestic violence would likely be a misdemeanor
if there were no injuries and no weapon used. But domestic violence is a broad term under which could fall many different types of crimes, so I cannot get more specific here. If this one were his only charge and it was a misdemeanor with no injuries, he would likely be able to resolve this without jail, assuming he were interested in a plea bargain.
The fact that he had a set of keys and took only his clothes might provide him with the makings of a defense to the burglary, but it won't get the case dismissed, particularly if any of the things he took from his former place are in dispute (his things, but she wants some of them and thinks that they are or should be hers). However, although this may make out a burglary on paper, DAs usually don't prosecute something like this as a burglaries when what you have is an ex going back to his old house without permission to get his stuff. They almost always reduce them to a lower level offense.
Generally charges like these under the circumstances you describe turn into a non-incarceratory plea opportunity -- probation, with counseling and anger management classes and an order of protection on behalf of the complainant. However, as you can see, burglary is a very serious charge and I don't have at my disposal the facts that the DA has. So make sure your boyfriend has a lawyer if he's brought into court