She broke up with him because she heard him on the phone talking to someone else saying that he didn't love her, that he was willing to marry her because that's what she wanted, he'd do anything she asked, like he was indebted to her.
It seemed like he had only feelings of gratitude towards her and that he just wanted to go along because she saved his father. So, once she knew she thought it'll be better for both of them to go their separate ways.
Imo, he likes her in a more friendly/family way, but the fact that she saved his father made him take responsibility in her happiness. I also think that his family took a great part in it as everyone seemed to like her and told him how great she wasy, also she showed that she was interested in him. So I think it's just him 'sacrificing' himself to make her happy, but once she knew the truth she didn't want it. It is shown that he noticed that she wasn't sure about the break up and he still went along with it, and the fact that he didn't ask for answers or anything, he just took it, shows that he just wanted to do whatever she wanted.
As for the fl starting this fake relationship, I think it was in hopes of maybe helping him find out that he liked her as a woman/girlfriend not as a family. However it seems it didn't go right as he already saw them and didn't do anything, also in this last chapter he keeps saying that she's like part of his family.
Hope this helped^^

Can someone kind pls explain why the fl and her ex broke up, I don't understand the 1st chp and the recent chapter, since he's willing to marry her and like how he's kinda regretting on breaking up???? Ty ╥﹏╥