Because he is a creepy dirtbag. He used Meguro until he got tired of her. He lies to his current girlfriend. He has a rendevouz with his ex-girlfriend without telling his current girlfriend, and ignores his current girlfriend's text messages. He's scum.
Meguro should have just refused to meet the dirtbag. That would have been the best choice and the one in which the only person who deserves to be hurt would get hurt (the dirtbag himself). Unfortunately, Meguro isn't the sharpest knife in the kitchen.