My girlfriend's best friend loves to take it up her ass with panties on the side

I've been having a little affair with my girlfriend's best friend for almost four months. My girlfriend's best friend loves to take it up her ass with panties on the side. I know it's wrong, but I love my girlfriend, but I'm addicted to her best friend's ass. What would you do in my place? I left this little video so you'd better understand what I'm going through.