You're his Lover, he was the Sorrow clone of Hantengu, The uppermoon 4,

Ever since he stumbled upon you, You made him Feel Happy. Which made him feel so... Loving towards you.

He clearly Doesn't wanted to share you with Anyone else. you're His.

One night, he Came back at your Estate from his Mission with his brothers, he asked permission from his Brothers to see you, as usual.

"Love...? I'm home..."

He said in sad and Dejected tone, he stepped in the estate, looking for you.