1) Lennie is dependent on George because he's a little on the childish side. Lennie's irresponsible, forgetful, and all around slow upstairs in the head. In a way it seems like they both had a rough life or a hard time growing up.
2) I think that George continues to keep Lennie around because he has to watch over him and be his care giver. Although, in a way it seems like their two brothers who lost their parents and now George is basically the the father figure in Lennie's life or atleast trying to be. Lennie seems to be all George has left and I think George loves Lennie to much to leave his side.
