Let me guess... Aunt dies. FL has given up trying to make him fall in love with her so it's worthless, then she fills up the divorce papers and puts it at home for him to sign the rest and hand it in. She packs her things and probably went to America or something (the first chapter shows "Hello-" in a different font, indicating she may have moved out of Korea). She used his money to open up a shop business.
As for ML, he comes back and can't find her. After months or few years of searching her frantically, he found her and angsty happens. To prevent him from hurting her any longer, she fakes herself to be married at the end of the year but ML refused to budge. She has a male friend to help her out and then ML gets jealously and force-kisses her. FL's pushes him away and tells him to stop bothering her when he doesn't love her to begin with. ML actually likes her but can't explain it to her, more angst 'till they finally solve the whole god damn thing.