How to get over someone without closure?

Long story short, in 2010 I had a huge crush on this guy at my school, but he and I couldn't really talk because of the age difference. However, from his body language, he seemed interested. I know this might sound crazy, but six years later I still think about him, but I don't let that stop me from living. I've liked other guys after him and been with other guys after him, but he was different. I should also mention that I haven't seen him since 2010. My closest friends call me crazy for liking a guy for this long, but I just need closure. So there's this girl on my Facebook that sort of knew him, and I want to ask her about him. But the thing is, I haven't talked to her since elementary school and now we're in college. I don't know what to do. If I should message her, what should I say?
How to get over someone without closure?
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