Why did he break up with me?

Me and my boyfriend had been going out for about 2 and a half months. We dated for about 4 weeks before we even decided to go out because both of us had been in bad relationships before. This one weekend I went down the shore and those same nights he went to the bar and over his friends house. Stupid me was a little unsure about ti so I asked him and he got really mad. I called him that night and he said he wasn’t going to break up with me so I was fine. The next few days were going okay, but not that same as before. I always asked him if anyhting was wrong and he nodded with a no and never said anyhting. The night before he wanted time alone so I gave him time…then he asked me to come over and everything was fine as it always was. The next day I get a text from him saying that we needed to talk. He told me he wanted to break up because he was unhappy ever since that night I said something about him going out those nights I was at the shore. And he was tired of seeing his sister unhappy because of us. Then that was it. I havent heard form him since and I jsut dont get it. I ahd no sign of any break up and he just left me like that. Now I am going to Cali tomorrow for 2 weeks and he’s known about this before we started dating. I jsut dont get it. Was he scared or did someone say something to him to make him break up with me?