Both Kenny and Lily have their flaws. Kenny hasn't directly killed anyone (Lily father was pretty much dead) but he would do so without a moment hesitation if he thought his family (now dead) was in danger in anyway.
Lily breakdown seemed forced on my playthrough because I was fair and kind to Lily throughout the game. But the fact of the matter is forced or not she did murder a gang member in cold blood. I don't want her anywhere around Clem. Not only because she is a murderer but because I can't trust her anymore.
The only way it makes sense to support Lily in episode three is if you metagame because it doesn't cost you anything (except your soul) and could work out to your advantage should you cross paths again and need her support.
Carley and Kat were the only two characters I could trust and held the group together. With them gone fuck Lily, Kenny, and the new people. I'd leave the group if I could. I don't trust anyone left, in fact, I almost count on the fact "a unhinged Kenny" and "a moron Ben" are more trouble then they are worth and are going to fuck over Lee in someway.
It's Lee and Clem against the world from here-on in.