The first one is easy it's A, no doubt. I have a friend who has 2 girlfriends, he has his own place and while neither live with him, both pay half the rent for him. Crazy, craziness and he cheats all the time and I've met them both. No way I would ever say anything and I pay extra attention to not slipping when I'm drunk or high.

The second one, it all depends. If it was a sick, premeditated murder where the details disgusted me and it was found out that my friend wasn't who he thought it was then yeah. Most likely I would just advise him to leave before police started knocking on my door.