What do I do? - " I don't want to destroy my brothers heart as well.."

Well, my brothers wife doesn't love my brother anymore, and she wants to go back to her old days of having fun, I explained to both of them that whatever they do, I'll support each of their decisions.

Well, one day his wife started to text me saying shes enjoys sex scenes and how they turn her on, I explained nearly the same thing out of being honest.

Then we started getting deeper in our conversation of what we like, and what we don't and what we would do,. (were literally best friends) but at the same time, she is married to my brother, and she doesn't love him anymore.

I don't make it awkward, or anything, but strangely today they have both been ignoring me.. Shes moving back to Washington in a couple weeks, and never to return.

I really do like her, and care for her, but I don't want to destroy my brothers heart as well..

What do I do? I apparently have more in common with my brothers wife, than he does, and I have a thing for her.

I don't know how to stop this kind of relationship, because its tearing me up inside. I don't want to ruin me and hers relationship, and at the same time,keep a friendship with my brother.

What do I do? Please help.