There's another old saying, "If you love something, set it free ... if it comes back, it's yours ... if it doesn't, it never was."
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This is so true, but hard in practice. If a person expends energy retrieving another person, they may regret it later. The onus would be on you to 'hang on' to him and there would always be the sneaking suspicion he may want to leave again--or the reason he wanted to leave would never be fully resolved.
Not only would I not make contact again for any reason, but I'd really want some serious explanatory convo, if he decides he wants to return. Not an inquisition, but a real in-depth talk about what his reason was--and how it has been resolved.
Life is so short, dear. Though it may not seem like it when you're younger--it is better to be alone, than unhappily together.
Good Luck!