we broke up

so i was dating my “ex” for almost 9 months. (im 17 he’s 18) i was so in love with him, still am. he’s literally the perfect guy. but almost a week ago we broke up because he recently left to go to college 1200 miles aways from where i live. i didn’t want to break up because i thought we would be fine doing long distance but he didnt think it was a good idea so we ended up breaking up. i’m devastated i haven’t stopped crying since the second he left. i dont know what to do i’m terrified of anything getting in between future plans. this sounds kinda crazy but i don’t want to ever see him with another girl i think that would actually destroy me. i can’t help but think about him 24/7. it’s honestly put a toll on my mental health, i’m always sad now. (im not suicidal or anything bad like that) but i just wanna be happy and normal again and idk what to do :(