The whole point of Lin/Big Mom is that she causes harm while thinking she is doing good. She uses it to justify all the horrible things she does, she's just more childlike with her memory gone. She's someone who thinks postive intentions make evil acts not-evil, unlike the Straw Hats who, for the most part, try to see things as they are
When the two of them started acting lovey-dovey, I totally expected it to end with them chased by police and committing suicide together (or some variation of this), which in some small way would be almost the closest you could get to closure + a "happy ending" to me where they both die in love and Sangwoo's killing ends.
This story ending open-ended like this was perfect tho.
Love stories like this, give or take a few elements, but waiting for new chapters can be painful. Off to read some other things again....