Open Question: why do i get jealous over the stupidest things?

my friend asked me to hangout today i said i couldnt so she hungout w/ my boyfriend and this wh-ore that likes my boyfirend.. he didnt ask me if i wanted to hangout and they had so much fun while i stayd home with my period being worried about how i hav to go back to counselling soon.. he also said he was annoyed @ me because i told someone something i appparently wasnt supposed to