I think my son and his gf broke up...

My son had this girlfriend for 2 years. Shes in a lot of our family pictures. Hes 18 and has been with her since he was 15 almost 16. I came home and in any family picture with her in them he wrote whore on her face. I asked did something happen between him and his girlfriend and he said "What girlfriend? Cheating whor- I mean Chelsea? Yeah we broke up. It's fine. I'm fine." I said "Really? Because you wrote whore over face on all her pictures." And he yelled IM FINE!!! How long should I wait before I try again to talk to him about it?