Nemurenu Yoru wa Ubai ni Kite ne

Ritsu's always had a special someone since he was a kitten. That special someone was his kind-hearted owner, Nagisa. To Nagisa, Ritsu's his beloved, irreplaceable cat... Or so Ritsu thought, until he walked in on Nagisa showing someone else his love. He runs away from home out of shock and meets Senju, a stray cat. Senju tells Ritsu he'll make him forget Nagisa. To top things off, he promises Ritsu he'll be his first when his heat comes... Just who the heck is this cat!? This is a comic about a doting prince-like well-endowed cat and a naive and sheltered cat being consensually taken from his owner!

(Source: Renta!)