Agreed with poet1234. You don't seem ready for a relationship of this sort (semi-long distance).
I'll add that it doesn't sound like she is ready, either. The fact that she is telling you all of this openly is a good sign; however, it seems that she needs the validation of this guy's attention more than she needs you to be comfortable. Have you addressed this new concern with her, or did you let it slide like an "alpha male" "would have done"?
Talk to her. Explain calmly that this bothers you, because it broke you two up in the past and there is no reason to think it won't happen again (they were "just friends" before, too). If you get the feeling that she is willing to let you remain uncomfortable just because she can't deal with NOT having this guy's attention, bail. It isn't worth worrying about.