Here's my take:
Sam didn't call Frank. Either Bonnie or Annalise had Frank follow Lila, saw Sam leave and then went up there and killed her. I believe Frank called a divorce lawyer?? Just not Frank. He is too loyal to Annalise.
Did they say Oliver had HIV or was sick? I thought he said he was sick which doesn't neccesarily mean HIV.
I have no idea who killed Rebecca, but I don't think it was Annalise or Frank.
I think Annalise will get Nate off, not just in bed!