She doesn't actually look like Sangwoo's mother, it's just Sangwoos deteriorating health is causing him to see his mum in the woman. His relationship with his mother from what we see, was pretty codependent and thus abusive, which has left quite a traumatic legacy. Sangwoo's relationship with women as a whole might have been influenced by this, but it's also maybe important to note that it is his mum who is in his nightmares and delusions (like the ski scene), not his dad, despite his dad apparently also being abusive. The importance of the impact his mother had on him, and which has left him this way, cannot be understated.
Spoiler
The most exciting in chapter 42 was the hug. The manga is still slow. I wish there will be a twist soon.