turns out my best bro has a crush on my crush . and guess what ? she like him back , and they 're going on a date tonight well you should be happy for them ! oh , you too ? does everyone get to have nice things except me ? no , but if you really liked her , you should be happy that she found someone she like . how about he thinks about me sometimes and how about she learns to like guys who are actually cool ? ?
The cause of the jealous feeling is the romantic interest being reciprocated by the crush towards the person's best friend.