why does my boyfriend do this in public?

I went with my friends to my boyfriends track meet (hes a football player so they have to do track in the off season) and after he ran, he came to sit with me in the bleachers and we were cuddling and what not and at first he put his hand on my thigh, then he started to move it closer to my vag. after a while he started rubbing and he was basically jacking me off right there! none of my friends noticed cause I was sitting at the end of our group. so I wanna know…y does he do that in public?!?!? I had to literally keep myself from screaming in pleasure, cause ya I liked it, but that was prbly the most inapproiate place from something like that to happen so WHY?!?!