More than friends?

So for the last 2.5 years, I (28m) have been good friends with this girl (24) I met in my course while working on a group project together. We really hit it off and have a lot of interests in common, mesh well as people and what not and have become best friends to the point where I don't think we go more than 48 hours without talking. When we met, I never really humored the idea of a relationship as she already had a boyfriend and both of us were just so damn happy that we made a friend. It was the easiest thing in the world to just be friends with her.

I learned that earlier this year that she had developed a crush on me and that it caused some problems between her and her boyfriend, she said that they dealt with it and had moved passed it, but it still made me profoundly uncomfortable being "the other guy". That discomfort came up during a trip away with our group about a fortnight ago where she indicated that she "wished she had me". We agreed not to talk about that as she was drunk at the time and a little upset.

That upset it turned out was because her relationship with her BF had turned sour and after coming around to unload about it, she decided that she was going to end it (I had nothing to do with it other than being a soundboard for her.) It's been rough since then and she's feeling it being alone for the first time in her adult life. She's been leaning on me for emotional support which... I'm trying my best to provide, but until today it had just been me, she's only just started going to our other friends for support.

One of those other friends *I* have been going to for support (or just to unload a little, I'm so grateful to her for helping me out.) But this friend kind of warned me that G(24) might be interested in me and that I should just be aware of that and not do anything stupid. And as much as it's a little awkward to get my head around, I think she might be right and my best friend might want to start something with me.

I have all sorts of issues processing this. Not least of all whether or not I'm imagining some attraction she has for me, or how selfish it is for me to be thinking about this while she is still in the midst of this breakup and needs my unconditional support. I don't like the idea that I might be the reason they broke up (him not trusting her with me was one reason) or feeling like some opportunist just hanging around and pretending to be her friend. I'm not sure I want to be the rebound or the replacement, nor am I really sure how to go about considering how much I might want a relationship with her, I certainly like her as a person, she is one of only a few that I just truly enjoy and look forward to being around.

There is a very real possibility that she comes to me with this at some point, and I'm not sure that I have a good plan for what to do if that happens. Any direction here would be greatly appreciated.