Well, the clingy behavior definitely would push any ISTP away, and just about any other type as well. It would probably push even me, an INFP, away! Based on what's transpired, I think your relationship may have gone to a point of no return.
It did start out promisingly, and must have been very passionate for him to have proposed to you, but it just wasn't in the stars for it to work out. Long-distance is extremely difficult, especially for ISTPs who are very sensory and spontaneous.
It sounds like first love, because it seems like it's very difficult for you to let go. My first relationship was long-distance with an ESFP and it was very painful as it ended. The whole "there must be a way to solve this" belief sounds very familiar to me. I was always the one convinced problems would work out ("I'll fix myself!"), while my exes wanted the simple exit. (Ironically, now I'm in a relationship where I want the "simple" exit and my ISTP thinks it'll all work itself out.

) It's never simple, though.
I would give him his space (no contact), which is what he's asking from you. Maybe that will allow him to come to you of his own will. Try to give yourself the love you so want from him. It's true that we're not ever fully ready to be in a good relationship until we can love and accept ourselves completely. If you're looking for validation from others, then that complete acceptance hasn't happened yet.
A bit of random advice that will be useful to you:
- Don't take things so seriously.
- Create your own happiness, your own sense of wholeness. No guy defines you. You define you.
- Be yourself. Love yourself. (I admit I'm still learning what this means)
- Men are like buses, there's always a next one.
Maybe you can call your best friend and go on a trip together to get him out of your system for a while. Find yourself again. You did have a fine life before him.
