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Smart people are so daft.
Neither guy is the right guy! The guy who moved out knew what was up and saved himself, you didn't think he was good enough for you and he knew it. You miss him because he was around for a long time but if he came back you'd get bored and frustrated again that he's not getting his masters and sits around watching the Simpsons. Plus sexless in a year, not a good sign anyway.
Now the man who returned from China, well if he's about to enter medical school then do a residency he's going to have slim time to rebuild a broken relationship, so maintain him as a friend but go out and live your single life for a while.
You're about to move away for a program, leave both these guys behind and keep the fond memories and what you liked and didn't like. There will be new guys in grad school and your new town.
Being smart, being interested in helping other people doesn't mean you are going to never hurt people. People's hearts get broken, being smart and well meaning doesn't mean you make the right choices all the time.