I'm so confused, frustrated, sad, don't know what to do!

Hi everybody, I'm going through a really tough time right now.  I broke up with my ex-girlfriend about 3 months ago after a 4 and a half years relationship.  I know I hurt her a lot breaking up with her before this time and then going back to her when I felt alone, among many other things.  I never cheated on her.  We started dating when we were both 16 and after a year we both lost our virginity to each other and we haven't been with anyone else sexually to this point.  Now I'm trying to get back with her but there's no doubt she doesn't want me back right now, she's dating another guy and told me that she's doing this to try to get over me, to see if she can kill the feelings she has for me, and that no matter what i'll always be the love of her life. I've been very depressed, and got really upset when I found out she was dating another guy, so I told her I didn't want any contact with her, I didn't want her to call me anymore, or visit me, or e-mail me, until she figured out what she really wanted.  Until she figures out if she wants to be with someone else for sure or if she wants to come back to me.  The problem is there was really no closure because of the fact that she told me that she's scared that nothing with this guy is gonna be the same as it was with me and she's gonna want to run back to my arms again; and she's scared that i'm not gonna be here for her if that happens.  Now, I really want her back, but i'm suffering so much knowing that she's going out with another guy and I can't get over her thinking that she might come back.  What should I do?  Wait for her to come back and in the meantime keep my mind busy? or just get over her and if she ever comes back just say no?