What options does college dropout with great grades, research projects and CV have to return to university (or thinktanks)?
I'm with @rocinante here: you're handicapping yourself if you can't get past whatever block is preventing you from discussing this personal issue with people from your past university.  I don't know whether it's embarrassing or emotionally painful (and you don't need to tell us, we're just yahoos on the internet), but you have to be able to give some account of it:


First of all, you should make a good faith attempt to finish your degree at your old institution.  I'm sure you did burn some bridges there when you left, but if you can't get past that to try, that doesn't sound especially driven to me.  Credentialism may be a little silly, but you're locking yourself out of a lot of doors if you don't finish your degree.
Also, if you want to be successful getting a position in any area of research, recommendations from "one of Europe's top ranked universities" would be pretty helpful (for getting into a graduate program of any description, they are essential).  I know less about think tanks, but in most graduate admission committees, even with a completed bachelor's, no letters from professors you had as an undergraduate and an unexplained gap in your transcript  that's not explained extremely well in your personal statement would be an immediate disqualification.  So, not only should you go back to your old university, you need to set up meetings with the professors you disappointed, apologize sincerely, explain your situation, and knock their socks off with where you are now.