By dating one of his friends or one of her ex’s. It’s only fair. LOL

And women don’t generally go after their friends’ ex’s. Girl Code. Not a very good friend. Or one you could stomach being around if she actually accepts him. Are you sure his ego isn’t getting the best of him? As if he could pick any girl (your particular friend) off the rack? Or he’s not trying to make you upset/jealous/sad?

You could have him promise you to not rebound after your friend and have her make the same promise.

Asking yourself to become OK with this now is a little over the top unless it’s, say, ten years later.