Help

So last night my boyfriend of four months decided to ignore my texts and calls. At first I thought his phone was dead but later found out he was just ignoring me. After worrying all night and morning I finally heard from him. We talked for awhile on the phone until I decided to go over to his house to talk more. When I got there he was apologetic just saying he was thinking. Then I noticed a hickey on his neck. I found out he was drinking and he says he doesn't know how he got it. He swears it was just him and two female friends and one of their boyfriends. I don't think I want to break up with him but how do I trust him again? Does anyone have advice? Should I stay stay with him? I feel he is being protective of his phone...