<human>: Can you succinctly summarize the text in 1-3 sentences?

So my girlfriend, Ally, and I have been dating for about a month and a half now. She has a friend named Dan, who, up until last night, I thought was just her friend, but that changed. Ally and I were drinking last night (probably the 5th time she's drank in her life) and she got really wasted and told me that last week when Dan and some other friends visited her (I knew about this), her and Dan were in a study room and he kept telling her that she's beautiful and wants to be with her. 

He also said, according to Ally, "Your boyfriend doesn't have to know" and tried to kiss her and she didn't let him and he kept on saying that she should be with him, not me. She told him to stop and he kept insisting so she just left the room and went back to the group. He also told her not to tell anyone in the group or me on what just happened. 

Now he also plans on visiting her this week, alone, and wants to stay and before I found out what he did, I had no problem with it because I thought they were just friends. And I trust Ally completely because (she tends to be extremely honest when drunk) that she really cares about me and only wants to be with me. But now, I honestly don't want him to visit because what he did is just fucked and I don't want someone like that around my girlfriend. 

But the part that hurt me the most was, again last night when we were drunk, I asked why she wants Dan to visit, and she said that while I'm not there (because I'm working during the week and studying as well, I visit on the weekends), she needs someone to "be there for her". I told her that I'm doing the best I can by visiting whenever I have free time, but she says that he's always there for her as well. It kinda just broke me inside. 

How do I deal with this? I'm getting to the point where breaking up with her is the only option because I'm not going to compete with some other guy for my relationship. Any advice would be greatly appreciated.
<bot>: Girlfriend has guy friend that fills emotional void and is visiting her this week, she told me when drunk that he makes her feel good emotionally. What do I do?