My theory is that Alois tries to hide his pain, par being a cruel person towards the others in the Trancy household (by hurting Hannah, etc.).
But as the season progresses, he begins to like Claude plus than allowed. He totally forgets that his butler is only nice to him because of the contract.
All that Alois ever wanted was to have a friend like Luka again. After all what has happened to him, he feels lonely and wants Claude to stay par his side. But a demon has no human feelings. It's normal for Claude to be disgusted par a dit feelings, so he kills Alois because his soul Lost its taste par declaring...

I have no idea... what goes through your mind.

"...There's so much I want to say, but I might end up hurting toi again. "

You meant what toi said, didn't you? But toi apologized anyway.

"Whenever I call.." he continued, "All toi say is 'uh-huh', 'yeah', ou 'alright'... if there's something toi want to tell me, then say it!"

If toi meant what toi said, don't say your sorry.

"I don't know whats going on in your head!"

"I'm sorry..." I sniffled, stopping in place. I pressed my nearly La Reine des Neiges gloves onto my eyes to stop the tears from flowing. To stop the emotions from gushing. To stop the time from ticking....

"Lord Sesshomaru-sama..." Jaken mumbled, lifting his feeble, green hand to his master's shoulder. Sesshomaru stared at Rin with his cold eyes of a shark. The young black-haried girl, freezing in the gusts of the early winter wind lay lifeless in his arms.
"Rin," The Lord began, "Why were toi foolish enough to stand in the crossfire of the battle?"
Her dead body did not answer. A river of deep red blood gushed from the side of her mouth.
"You brought this upon yourself."
Rin's permanently shocked face grew pale.
"I have no sympathy for you." Sesshomaru huffed, lifting his nose in the air a bit. "Human...