I like my best friend's boyfriend.
In what kind of way do you like her boyfriend?
He's sarcastic and he makes me laugh very hard even when I'm sad. Most importantly, he listens to me when no one else does.
It isn't okay to feel romantically for your best friend's partner.  That is a huge betrayal.  You can be friends with him but not a romantic interest.
I know but it's easier said than done.
I understand it's hard to get rid of feelings for someone but it must be done. Maybe you should find another guy to date?