Since this is your wife's best friend, I would assume that even w/o the dating potential, you would offer your home to her to get her out of an abusive situation.
We've had friends stay with us as needed through out the years; occasionally there was some cross over benefits of said arrangements with the intent of keeping the friendship intact.
I would urge caution about the boyfriend though. If she is considering leaving him, for any reason, he may become more abusive and lash out towards those helping her. Just something to consider. Good luck.