2 Corinthians 6:14-17 AMP

I've heard all kinds of definitions and applications for being unequally yoked. What does it mean to separate ourselves? the phrase "guilty by association" comes to mind. is there a Biblical basis for that saying? does anyone in the Bible set an example of this? what about Jesus? obviously He did completely stay away from ungodly people. one of the major complaints against Him was his "hanging out" with sinners. where did He draw the line?