Linda has a lot of explaining to do, not you. Yes- have a conversation with her, and let her know that you won't put up with her beau's crap, especially on your Facebook page. If no apology is forthcoming from the man, then de-friend him. And if Linda wants to apologize for him, that is simply not good enough- she is then just enabling him. And do you need that kind of 'friend'?
Be the love you seek.