I wouldn’t be too hard on yourself. If that’s not your orientation or something you want to explore that’s fine. I’d deal with this issue the same way I’d deal with a friend that’s gay. Sex is off the table. You wouldn’t sit around and have your friend make advances at you. It just wouldn’t come up. Your friendship has nothing to do with what they do behind closed doors. The same thing applies here. The fact that they swing is of no concern to you or the friendship. You don’t even want to know the details, as long as they aren’t doing it with you!