I miss him and I don't know what to do, please help!?

I have just come out of a serious relationship (about 2 years) and it was me who ended it. I left him because I think that I need to experience life more (as I am only 18) and need to find out who I am as a person. I still love him to pieces and it is killing me inside to do this to him, as I know he is infatuated with me. I feel like a horrible person and am so lost as what to do.