I miss my ex, how can I get over him?

As I mentioned above, I miss my ex. He recently moved to a different country and the fact that I might never see him again in the future saddens me so much. I thought I would be all happy once he leaves. But that wasn't the case. I might forget him eventually but I'm just sick of myself dwelling on the past and missing him when I really shouldn't. I'm a senior and I'm graduating in a few months and so is he. I guess I just didn't see this coming since it's pretty abnormal to move before the last year of high school. Some of my friends told me to just text him and ask him how he has been and stuff, but I just have no courage to do so as we haven't talked in almost a year. I'm pretty sure he has forgotten about me and is happy without me. Should I just message him one last time; wish him luck and tell him my honest feelings towards him , or forget about him and let him go. It just isn't easy for me to let him go that easily because I've known him for so long and we have had a lot of good times together.
I miss my ex, how can I get over him?
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