My ex boyfriend broke up with me out of the blue because he thought it wasn't right for us anymore. I then moved onto a rebound guy and I don't really have feelings for him but he is infatuated with me. He just gives me the attention that my ex used to give me. The reason I don't like this guy is because I still have major feelings for my ex, but my ex thoroughly does not like me anymore. But this rebound guy is borderline obsessed with me. I know the right thing to do is cut off the guy but I know if I do that I will
1. Feel insanely lonely
2. Never get over my ex
3. Feel like I have no one and start to feel bad about myself again.
I truly don't know what to do in this situation.

I think time for yourself to sort yourself out, and properly heal, is what you should do. In this way you can work on your own personal issues, and maybe learn to deal with YOURSELF and break your unhealthy dependence on a relationship or other people to feel good about yourself.

Obviously you should build a life that you enjoy without a boyfriend to give you attention.