The only thing that gets me about this episode is how Clark gets all in Lex's face about lying and keeping things secret from his friends. Like Clark has been doing that himself. Hypocrite.
I know Lex Luthor has to end up "evil", but based on what I have seen on the show: how everyone treats him and automatically assumes the worst, it's no wonder he does turn into villain.
I hope that Lex being "evil", is not so much him being a BBEG, but a person who is still friends with Clark Kent, but does things that a "morally questionable", at least in the eyes of Clark.
Repeating something along the lines of what Henry posted in another thread, it could be the reason that Lex goes "evil", is that Lex Luthor was failed by Clark Kent (not treated as a true friend, etc.) resulting in Clark Kent spending the rest of his life as Superman dealing with that mistake.