I think he is seeing someone else. OK, so he was home.. you don't know if he was there alone or with someone. My guess is, he was probably with someone. whenever a guy changes his attitude towards you without warning, it's almost always b/c he is interested in someone else. If the 2 of you are close, you should be able to talk to him about anything. If you can't, it never would have worked anyway. Just tell him to be honest with you.. that you won't get mad but need to know the truth. He might tell you, he might not.. but if he continues to be distant, you need to move on & leave him alone.. take a hint.