Straddeling my boyfriend while i make out with him?

we were hanging out at my bfs house his parents were not home so i went and hung my bag up because it was wet from swim pratice so i had to hang it up beside adams when i came back into the room he was sitting on the couch so i decided to straddle him well we were making out and we were grinding really hard i could hear him moaning did he finish or did i give him blueballs because we were getting really into it and his mom pulled up in the drive way so did he finish or not and another thing why do guys like that so much if he didnt finish wont it hurt or is it worth it