Do i have a disorder? Why do i get so depressed and lonely when my friends leave?

please dont mind rhe mistakes im in an ipod....Ok so i just left my relay for life and it was so fun and it was on the on eyear mark of mine and my boyfriends anniversary. This happens all the time and i wanna know if i have a disorder. I left and my friend came back home with me but left at 5 abd as soon as she left i got the worst feeling of emptiness an just started getting upset. This happens all the tome i am with my friends for a lon amount of time and leave the fun. I get seriously upset too like loss of appetite and Crying. Whats wrong with me?