You do know if he fucks her with his big cock he will own her and you won't be fucking her again. That's how I met my husband, his big cock is sometimes too big for me after all these years. I just love how big he is so be careful what you wish for.
Just suck his dick bitch.
#1 has a point and many similar stories on here would vouch for that if they can be at least partially believed. My wife sleeps with other men and I sleep with other woman, usually at the same time, but she's also addicted to me the person and not just a cock so I'm not worried. Trust me, a woman who sleeps with another man as part of your couple kink but ditches you for the well endowed guy obviously didn't think much of you to start
with.