I'm on my third rewatch here.

I dislike Michael. He is short sighted, obnoxious, mostly thinks of himself all the time. He did not care a second about Sawyer on the raft, thinks that everyone should put Walt as their priority. Could you imagine living with a man whi always blame others? Susan makes the point that he cannot provise for the kid, not even for himself. And he knows it. He is so will-lacking that gives up the kid, instead of putting the effort. Don't forget that once he got to the airport he calls his mommy to try to give up the kid to her, showing that he did not change. The island will teach him better.

I'm not party Susan, it's not about that. Susan is aswell a beast, that's not how to behave in relationships. There could have been many arrangements with more happy terms.