Why do you think he deserves love? Tell me what he has done exactly to be deserving of love. I am asking you to name a time when Sejin has done something that made him lovable.
Sejin is an incredibly passive character, he does very little in this story. Most of what happens happens to him and he doesn't react to it. He's made two decisions and only two decisions and this entire manhwa. He has taken action twice.
1. He stole from his husband because he thought he would be rewarded by his family.
2.He continued to hide the theft even after realizing he was not going to benefit from the theft. He knew that his husband could mitigate the damage the theft caused if he told him, but he thought he would continue to get more out of the marriage by hiding it.
I cannot think of a single thing that sejin has done that is lovable. He mostly just sits there and that's fine but it doesn't make him deserving of anything. The two things he's done make him deserve prison, not love.
If your husband stole from you the way that Sejin stole from Ido you would divorce them and testify against them to ensure they went to prison. We all would.
This hurts so bad, Sejin deserves so much love!!