Help

Hi guyz , can someone help understand my situation? So i have been with a very serious relationship with my bf, i am 31 he is 25 , i am the bottom but i take care of the relationship , u ca say i have the lead, and he is the fucking hot jock top who fucks and do as said, i am very jealous , the extreme kind of jealous, that sometimes gets pissed off of him for talking to normal friends , but i dont know why i have this fantasy for him to fuck and dominate another bottom, not getting intimate , just getting sucked and fuck the shit out him, i even told him and he said as long as he has me then his dick will not touch another, can someone tell me why i am jelous but love to see him destroy another ass?