I cheated on my gf because she damaged my car...?

We got into a fight and she threw my favorite jacket out the window. I called her a slut and she got all pissed and grabs the stones outside and starts throwing them at my brand new 1986 Honda Civic. I met this girl at the gym later and slept with her to get revenge on my gf. is this justified? After all, she did throw my jacket out the window and damaged my car.