Readings & Meanings:
reverse side, back, opposite
It advanced in secret.
He's a double-dealing guy, so I can't trust him.
Did you see the principal's wearing his pants inside out?!
The guy that she was dating for a very long time betrayed her, and she committed suicide.
亠, the pot lid Nabebuta, is on top. We discussed this in 育
衣, clothing, is on the bottom. See http://sokasoka.blogspot.com/2008/02/folds-in-your-clothes.html
里 is in the middle, the belt (of land) kanji we pointed out in 埋.
Okay, so "belt," "clothes" and "lid." Kanji Networks says "As per 里 (Type 1 Phonetic) (belt of land) + 衣 clothing → strips of fabric used as lining/backing material for clothes → back; reverse; opposite; inside. Extended meanings include (in) secret, behind the scenes, the sole and the bottom half of an inning."
Fair enough. I still don't see the connection between 里 and strips of clothing, but I'll deal.