Why is letting go so hard???...

Why is letting go so hard???... No matter what I tried to do, I’ve tried to let go. I know it’s been almost two years, and I know I should have let go of the past by now, but it’s so hard. I have tried so many things; like move away, dated different girls, and keep myself busy, but nothing has worked. There are times where I wouldn’t talk to this certain girl for many months, but the moment I see her, I don’t know how to act. I get so scared that I freeze up. What is wrong with me?!? The only thing I can think of doing is moving to a different country, but I’m risking so much. I cannot move away from my family for a long period of time. I moved to Las Vegas last year, and that didn’t work out because I miss them more than I miss this certain girl. I found out the only time when I don’t think about this girl is when I am in a different country. So is that the only option?