Stay in vague touch (at least keep an email address or phone number for him), clean up your life and get some stuff going that is good then invite him out to dinner. I'm talking 6 months or so, a nice job, place to live, a few interesting friends, etc., whatever you want your life to be like with/without him in it; get that as best you can (or on the way to that -- in school or with a job that has promotional possibilities, etc. -- some sort of 5 year (at least) "plan" for your life) and then try to incorporate him again :-)