I'd agree Ice.
It seems Angelbones as though your friend sees your sister in a very different light from yourself, and he has come down on her side.
I think it's a shame that you have severed all contact with your frinds though, after such a long time.
Why not write them a letter? Explain that you acted in your friend's best interests, and you are sorry if it caused a rift. Tell them that you value their friendship, and you hope that you can all get past this, and that your friendship can pick up again.
If you don;t hear back, you are no worse off, but you have done what you can to redeem your relationship.
Sorry this has not worked out, but as the government always says, lessons have been learned.