Having sex on a bicycle with two friends' girlfriends (RCT-600)

Sometimes, when I ride on my friend's girlfriend's bicycle, our bodies press tightly together, and I inadvertently get an erection! My body heats up, and I start rubbing her breasts from behind, masturbating by rubbing her underwear. While standing and riding, I play with her vagina from behind, secretly having sex with her while riding, even racing to see who can ride faster! And then, feeling betrayed, I ejaculate heavily inside my friend's girlfriend!