Marmalade Boy

Miki Koishikawa lived a normal life - until her parents tell her they'll get divorced.. She doesn't agree, until she meets Yuu Matsuura... the handsome son of another couple, with whom her parents are switching spouses. They all live together now in an enormous house, and Miki and Yuu find themselves falling in love. They'll have to struggle with their own feelings, other people who want to be with them, and whatever Lady Luck and Fate throws in their ways... (myanimelist.net)