How to get over "what could have been"?

I was in the situation where i was taken away from the person I loved. I was taken away from him when our relationship was a the point of getting serious, when we’d normally be labeled as “boyfriend and girlfriend”. We’d just been fooling around for about three months, knowing that after those three months we both had to go our seperate ways (we live in different continents). We never expected to feel that strongly about each other, as we said ourselves “we’re just enjoying our last time here, nothing serious”. But when it was all coming to an end I realised what I had to leave, and what I may not ever see again. I realised that i loved him. He was my first love and still, over half a year since we left each other I can’t seem to let go of the feeling of “what could have been”. what do I do?

Just for some consideration; we met up for new years eve 2010 in the country we both lived in during the time we were together. It was so great to see him again and all the feelings came back the minute I felt his touch. Is this something I should hold on to? I miss him so much