He's told you he just wants to be friends. What is wrong or missing in you that you'd not take that remark at face value and keep away from persuing him for anything more? You're ex's for a reason. In that short period of time I doubt either of you have changed much and lilkely the same issues that caused you to break up the first time are still very much present in the both of you.
Give up on him. If he wanted you in the same way you want him, he'd have been keen to have you since you laid our your feelings to him. The way things are now, if you carry on with him, you will be falling into bed with him and he's still just only want to be your "friend" but you'll be upgraded to "with benefits." Not much of an upgrade when you want to be his girlfriend that he loves and respects and is exclusive with now is it?
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion