Am I right to be mad at my online boyfriend for leaving to see his friends instead of talking to me?

Before I get into my question, I first need to say that my boyfriend, whom I met online, lives in a completely different country from me. However, we consider ourselves to be exclusive both virtually and in the real world and intend to be together in the future. We've known eachother about 5 months now.

Basically, last night him and I were talking on skype for a few hours. Whenever I get a day off work, and I can stay up late enough to talk (since our timezone's are quite different) we take the opportunity and spend time together. In the middle of our conversation he recieved a call, muted skype, and talked to his friend. When he came back from the phone he told me he would be leaving to go out to a bar with some of his friends from school. It wasn't a question, like, "is it okay if I go to the bar with some friends?", it was a statement. I was hurt by it because I had hoped to talk to him and was staying up later than usual to spend time doing so. He apologized for hurting me, and said he didn't want to upset me, but went anyways.

I just wanted to know if I'm being reasonable or overreacting on this one.