Basically Misato thought he was Akira's boyfriend until Akira pretty much told him he was just a replacement for the kid and thanked him for his time. Then he dates Mei for revenge, tries to dump him after a conscience attack and finds out that even the cute nickname he's got refers to the damn kid that stole the man that was supposed to be his boyfriend! Even after reading the other story it feels like Mei is holding on to him out of pity and waiting for the day when he'll actually love Misato...who he still calls Sato. Poor Misato can't even keep his own identity in all the deception going on around him.
Kyou Anata ni Wakare wo Tsugemasu