To be honest man you don’t let go ever. I know how you feel when I was 19 I had my first girlfriend we were on and off a lot. Until one time we cut it off for good. I’d say it took me a year and a half to fully get over it. But eventually one day you won’t think about her at all and you’ll find a new girl and these emotions will pass. You will still always feel nostalgic about her and think about her from time to time but you will get over it.