ok so jin seo revealed a documentary in which he reveals all the crime baek ah jin has committed, he did that to bring her back and in the end jun seo was going to suicide with Baek ah jin but in the end bake ah jin survived and junseo dead. and the series ended
but SML doesn't know her from Childhood, and the ML knows her from Childhood so he knows how to handle her or will she react, so I think so that doesn't count as a stalkerish behaviour