Genesis 4:16

"So Cain went out from the Lord's presence and lived in the land of Nod, east of Eden."  Genesis 4:16

So did Cain leave God or is that just signalling the end of their conversation?  Is this one of those instances where we don't like what we hear from God so we turn our backs on him?  Or is this just pointing out that Cain went out and lived as a wanderer as God had said he would?  The Qbible translates that lived as "married" and Nod as "vagrancy" or "wandering".  Although the land could have been named that later because Cain wandered there.  

I have to wonder who Cain married.  Was it one of his sisters that Adam and Eve had later?  Or did God create other people also?  Was incest wrong?  If it was wrong wouldn't God give them a way to "go forth and multiple" without sinning?  Are there things that were not sins then that are now?