You need to understand the real situation, because too many people are telling you what you want to hear. She didn't meet the rebound guy the day after you broke up. She was already interested in him, possibly already involved with him. And the reason why she is now showing some possible interest in getting back together with you is that the new guy isn't as great as she was hoping he would be. The "intense" relationship that she has with him is probably sexually intense, but otherwise not so great.
If you have any self-respect left, you will forget about her and move on. She isn't treating you with respect right now, she's trying to have it both ways: hot sex with the new guy and comfortable talks with you. The reasons for your breakup are still there, waiting to break you two up again and again, because neither of you have had enough time to change significantly. So just make a better choice and move on. Find a woman who wants you and only you, not you plus some other guy.
Good decisions come from experience. Experience comes from bad decisions.