Kanojo mo Kanojo

From Kodansha:
Naoya just got a girlfriend, the gorgeous Saki-chan, and though their intensities often pit them against each other like ice and fire, they're totally, uncontrollably in love with each other. He vows never to cheat...when out of the blue he receives another confession! Nagisa's cute, sweet and she's made him lunch to boot! He knows he can't cheat, but he can't let a cutie like this get away so he does the logical (?) thing: Asks Saki for permission to date them both.