Not into guys anymore?

Hello /r/gay i am an 19 year old guy that just a year a go decided to come out as bisexual. i have had sex with guys before and some small relationships and liked it alot. But yesterday when me and another guy got down to having sex i... i just didnt liked it as much as i used to. Im really scared of finding out that i am really a heterosexual cause belive it or not i dont want that. As i said i just started to come out to friends and family and everyone supports me. Could it just be that day/that guy? have you been in a similare situation?(sorry for my english)