how to get over someone ne i will probably never seen again?

I had a thing with a guy for about a week while i was on vacation in the summer . It was fun but after a week i had to leave the place and i never saw him again . I haven’t seen him in 3 months but i still miss him and think about him a lot . I can’t move on and i feel stupid because i know it’s over and i’m never going to see him again . I can’t like anyone else and whenever i try to like someone else my feelings for him get stronger . I felt very different with him and i feel like i’ll never get to feel like that with someone else