I also read the novel and that is hell of an exaggeration to say he "manipulated" her. Leila liked Kyle but also suffers from very low self esteem and social status of Kyle is a big intimidating factor for her. Kyle couldn't respond to that properly and instead of reassuring her of her worth as a person (which he believed in unlike certain trash ML) he tries to portray the things he can do for her if she allows him. This ends up worsening her social status anxiety but ultimately decides to trust Kyle as being Kyle and not the son of a doc. Kyle by no means was the trashy man in this story and if anything, he was too naively good to realize the harshness of her situations. You are pointing finger in a wrong direction when we have one of the biggest black flags in history of manhwa walking all over fl every damn encounter.
Leyla doesn't have low self esteem in front of Kyle, it's actually Matthias. This is pointed out early in the novel when Leyla was younger and Claudine has given her the gold coin for playing with her, the coin falls and rolls to Matthias' feet where he steps on it and Leyla has to retrieve it. When she bends down to pick it up and Matthias looks down on her, it highlights their respective status. Leyla has always been herself around Kyle so saying she has low self esteem around him is not accurate. Another example of Leyla's low self esteem around Matthias in the novel when she has a flashback of helping out a farmhand feed hay to the horses and she sees Matthias and Claudine taking a walk, Leyla notes that they seemed like a perfect pair and compares herself who is dirty from working in the barn, she hides from them because she was self conscious of her present appearance verses their elegance and nobility.
Also Kyle's discussion and agreement with his father for his acceptance of his decision to marry Leyla. Leyla also specifically told Kyle that she couldn't accept his proposal because she didn't have any romantic feelings for him, her feelings were strictly platonic. It was Kyle who couldn't accept it and continued to basically pressure Leyla. In fact in the novel it was Ms. Mona who convinced Uncle Bill that a marriage to Kyle wouldn't be a bad thing because Bill was initially against the proposal as well. And he could see that Leyla wasn't romantically into Kyle. He only gave his consent after Ms. Mona's input and then realizing that Kyle could give Leyla a good life.
There are some readers under the misconception that Kyle is this wonderful guy, but as someone who read the novel multiple times, I can tell you that the webtoon doesn't show it but Kyle basically emotionally manipulates Leyla into accepting his proposal with the benefit of attending college like she always wanted. In fact Leyla first rejects him and tells him that she wants them to remain friends because she does love Kyle in that way. Kyle keeps showing up at Leyla and Bill's cabin to propose everyday until Bill thinks it's not so bad if Leyla married Kyle as he is a good kid, Bill expresses this to Leyla who always wants to make Bill happy and as such accepts Kyle's proposal.