My 18yo son and his girlfriend have been fighting and I'm tired of hearing it.

Here's the thing, I think they spend too much time together and ever since school let out for summer, they have been getting into fights.  And I don't mean arguments.  I mean I hearing screaming and yelling and things breaking in the basement.  So I go in there and what is happening is my son's girlfriend loses her temper and she hits my son.  When I say hit, I mean she punches him in the face, backhands him in the mouth.  My son has a really bad temper, but he checks it and instead of hitting her back which is his natural reaction, he punches the wall or topples over his dresser, etc.

This morning they started in again, and she hit him in the mouth and he knocked her cell phone out of her hand.  So I went into the room and I told both of them I have had it and this crap of her slapping him when she is mad needs to stop and the holes in my wall have to stop.  The girlfriend then tells me she is sick of my son being such an a-hole.  I told them both that basically they are behaving like little kids throwing temper tantrums and when you become an adult you have to learn that you cannot simply physically throw fits.

I don't want to have to ban them from being together in my house, but if I won't have a house left if this continues.  Plus, I don't know what to tell my son as far as how to handle it when she gets physical with him.  He's confided in me that he knows men should never hit a woman, but when she has punched him in the face, he just really wants to hit her back.  He says she hits him knowing that he would never hit her.  So what am I supposed to say to my son.  That he should just sit there and let her beat on him and do nothing?  I told him maybe he should restrain her and then walk away from her. 

Not to mention, it's hard for me to work and play referee at the same time.  I have a 9yo here at home for the summer and she's much less trouble then the teenager is turning out to be!  I love summer!