I've seen things like that in my life too. I've had people treat me badly for years and not one of the people who said they loved me stuck up for me. I've wondered how bad someone would have to treat me before people in his circle stopped wanting to be friends with him.
It's something I've wondered and something I've been disappointed to learn the answer to as I've grown older. Here's the piece of wisdom I've garnered: A lot of people don't care how their friends treat someone, as long as they don't treat them that way too. As long as they reap the benefits they're getting out of the relationship, they will close a blind eye to what their friend does to others.
They may very well regret it one day but odds are, they will become more like the person they enabled. And yes, I said "enabled." Because any behavior we tolerate in a friend, that is hurtful to others, is something we have chosen to turn a blind eye to. The friend knows it too. And the friend is less likely to do anything about it because we, obviously, don't care.
Turning a blind eye to a friend's sin will come back to bite you in the end.....one day.....one way or another.
So, I've learned not to wait for a hero to come to my aid. There are few truly heroic people out there. And it's a sad, sad thing to learn.