Spoilerr
He want revenge on Michel family,
Ain is a bastard son of the North who was deeply traumatized and sexually abused by prominent southern nobles when he was younger, specifically Michel’s father. He harbors immense hatred for the hypocrisy of southern aristocrats, they present themselves as pure and obsessed with marital propriety, yet secretly buy, abuse, and discard young servants behind closed doors.
Ain’s original intention was to manipulate Michel, force him to fall helplessly in love with a "servant," use him, and ultimately discard him to completely ruin House Anatole but as the story progresses, Ian’s lies trap him as well. He is completely caught off guard by Michel’s pure, gentle, and utterly devoted nature. But Michel loves Ain regardless of whether he is a servant or a lord, causing Ain to genuinely fall in love with him
He was used like a prostitute by the men in the south including anatolds father. He planned to kill him at the cabin, but just like ch 31, he can’t do it. He’s going to treat him coldly and eventually fall for him and try to hide his dark past. He’s also a bastard child born from an affair, his mother was broken and remained delusional that his father would return. So Ian set out to join his father’s family, kill his father and katiyas mother, and go on to torment Katiya. I don’t believe he’s ever violent with anatold, but he does drug him to keep him asleep and does some inappropriate things to him. Besides that Ian is a very well done “red flag,” I’ve heard other novel readers call him the king of gaslighting -and that’s the best way I can describe him.
If u wanna read it u can buy the volumes on Rikki and translate thru screenshot or translating apps- I couldn’t find online translations for volume 3 & 4 (this season in the manhwa) so those low quality translations with require interpretation.

someone PLEASEE give novel spoilers as to why ain is doing this