We'd been dating for 2 1/2 years; she's 21, and I'm 22. We moved in together last May, and we started having a lot of problems around October. I was struggling with depression and acted like an asshole. We split up for around a week in February. During that time, she started talking to some 31 year old dude who would always come into her work. He started buying her gift cards for wine, and he gave her gas money once. Then she found out that he has a fiancee, so she figured he's just a nice person. She told me all of this once we got back together.
So, we decided to try to make things work and after some more rough patches, things finally seemed to be getting better. She told me that she did have a crush on this guy for awhile but that he isn't good enough for her and that I am.
Anyway, he would always come in to her work during his lunch. We've been wondering wtf his deal is and if he's just a nice person or what. So she decided to meet him at Sonic and talk to him and get to the bottom of things. I told her I was okay with that.
So she talks to him, and I ask her what he said. She said that he told her that he was attracted to her, and they decided that they probably shouldn't talk anymore. Over the next few days, though, she's been giving me more details about their conversation. She told me that she thought she didn't have a crush on him anymore, but after talking to him, she realized that she still does. Then she told me that he told her that, if he was single, there would "never be a minute that he wouldn't be between her legs" (this asshole knew that we were dating, too). I told her that I think he's an absolute creep, and she insists that he's not because he mows some old lady's lawn and takes care of his sick mom. We got into a fight about that.
I decided that the whole situation is ****ed up and that, since I'm trying to get over my depression, I don't need to deal with this bullshit that makes me feel worthless all the time (we've fought about similar things before). I really don't want to lose her, but it looks like I'm going to either way, so it might as well be on my terms, right? But now I'm wondering if I overreacted. What do you guys think? Am I justified in breaking up with her for this? Is that dude a creep or not?
tl;dr: My girlfriend developed a crush on a guy 10 years older than her, I got pissed and broke up with her. Did I overreact?