I (19M) got my dick sucked by my friends girlfriend (19F)

Honestly don’t know what to do here. I find myself being so guilty at times but it feels so fucking good sliding in and out of her throat. This has been going on for like a month now. She’s a sick fuck about it too, constantly talking shit about my friend and his dick size while she does it. It almost makes me hornier… I don’t know what the fuck to do.