if you can't stop thinking about your ex after five years and they have moved on would you tell the ex that you can't stop thinking about them and would like a friendship or something of some sort to get over your feelings seeing that you didn't have proper closure and still unsure of why the break up happend?
Instead of being indirect about this, try being direct instead. Send him a letter, saying that how your relationship ended bothered you, and you'd like to know his perspective.
Beyond that, I'd start talking to a therapist. Five years is a long, long time to be stuck on a relationship, and you might need a lot more closure than just finding out why he dumped you.
He cheated constantly. I dumped him. Does he care?
My boyfriend dumped me because I have chlamydia...why?