I think Marceline's relationship with the Ice King is really cool. The real father they gave her is really sucky so they gave her a father figure that actually cares.Or at least used to.The fact that the one person who really cared about her was robbed from her adds to her character.And she even still likes and cares about him too even though he dosen't even remember their history. It shows us that she cares and loves.Even at times when the person she loves dosen't love her back.

P.S.sorry for ranting last week