(Note: I apologize in advance for the length of my responses, but I can't help myself. I really relate to your story because we seem to be so much alike.)
Oh my God! I swear I am beginning to think you are like some alternate universe me, or something. LOL! I feel you so much, brother! I know, so very much how you feel.
At a time when this girl barely knows you yet, she is already professing a supposed deep and intimate love for you. In your head you know it is too soon to really be in love, but your heart wants that feeling so badly that you almost want to believe it can be true. I know how you feel so much. I've lived with that my whole life as well. The bad news is, it never really goes away, but the good news is that you CAN learn to better understand that in yourself. You CAN learn to allow yourself to enjoy that feeling, while also engaging your sensible side and realizing not to let yourself fall too hard too fast.
I wish I could tell you that transition is easy, but it really isn't. It is worth it, though. I am just like you in this aspect, so I know how hard it can be not to want love so badly you ignore so many red flags, almost to the point where you aren't even noticing them anymore. It's somewhat of a torture because it's like our hearts are constantly looking for that true love, and if you don't learn to control that, that can be dangerous. It can be dangerous because it can cause you to (whether you realize you are doing it or not) force something that is NOT a good relationship at all into being more serious than you should allow because your heart sort of tries to deny the problems.
I don't know about you, but for me it seems like any time I am not in a relationship, I almost always have a crush on some girl. I hate it and love it at the same time. Equally, if/when I am in a relationship, I have a tendency to get too attached, and think it is real love when maybe it is not. Thankfully, through years of life experience, I have learned and grown within myself. I am now aware of how I am and aware that, unfortunately, I will never be able to CHANGE that, but I can and have learned to better control it.
There is part of you that still cares for her because you sort of want to believe that love you thought you had was real. That real, true love feels amazing, and you just want your chance to experience that. I understand that. I know the feeling. The thing is, that sort of true love is something you cannot force. When you try, such as in this situation, you are only going to get hurt. You don't deserve that. Nobody does, but you, my friend, are a rare gem in this world. Your view of love is a rare gift that will some day make some girl the happiest, luckiest girl in the world. You just make sure she is somebody who deserves you. That isn't me telling you to be cocky. Far from it. I am just saying that you deserve somebody who cares for you as deeply as you are capable of caring for her.
You know something else? I don't think it is really all that strange that you were able to have such a deep connection with somebody you've not yet met in person. I do think you should learn a lesson from this experience and learn that a romantic relationship cannot work unless you can be together in person. However, I think the fact that you are capable of that is a good thing, not a bad thing. That is, a good thing so long as you don't let it get too carried away (as you had started to do in this situation, which is not your fault but I feel more hers for playing with your heart). Personally, I am equally capable of forming deep connections with people online, I've just learned through years of life experience that it can only get so deep unless you can actually be in person.
But, I think that is a good quality in both of us. For me, I can form such deep connections with somebody online because, when it comes to finding my true soulmate, I want her to practically be my best friend. I don't really want to just see some random girl I find attractive and ask her out. I'd rather know her first, form a deeper connection, and then ask her out. I sense that you seek out a similar connection. You don't strike me as the numbers type of guy to go around asking out as many women as you can just hoping some will say yes. I think that is a good thing, not a bad thing. You just have to learn to better identify when the person is so very much the wrong person.
She's playing games with your heart. Her throwing this other guy in your face is not right at all. For the sake of discussion, et's pretend even for a second that her intention isn't to play games and give herself an ego boost by having two guys fighting over her. Let's pretend for a second that she sincerely loves you both and cannot decide between you two.... Even if that WERE the case, her actions are still not okay by any stretch of the imagination. Even if that were the case, she'd need to decide and let one of you go. In this case, though, I honestly don't think that is the case. She's playing with you both.
I think it is awesome that you are even concerned for this guy as well. Maybe it is just my opinion, but I think you should just let him figure it out on his own. He probably will anyway. Fact of the matter is, though, if you tried it would very possibly just cause drama you don't need. You run the risk that he wouldn't believe you, wouldn't trust you, and it could just cause problems you don't need in your life.
Anyway, I have to admit, I am taking a pretty specific interest in your story here because you sound so much like me. Sometimes I feel like I am alone in this world, so I really like hearing that I am not. I don't really know if I can help you, or if my thoughts/advice/experiences are at all helpful, but I will definitely try. Good luck to you. As I said before, I sincerely hope you some day soon find a girl who truly deserves the love you are capable of sharing with somebody, and I hope she returns it just as strongly. You rock! I know what it is like having a low self-esteem, so if you maybe can't believe it enough to say it to yourself, I am going to say it for you. You are awesome. You deserve better than that girl. Don't settle. Go out there and find somebody worthy of you.