First of all, you are the best Jazkin!.
I like the art style and the fact that Doyeon and Junji are so unpredictables. It's been some time since I got so hooked up to a manga/manhwa. The story seems to revolve a lot around loneliness (I'm not projecting, right?... right?).
From the start Doyeon hints that she suffered from loneliness as a child, and her interest at Junji was because she felt her loneliness through the wall. Also, the reason she let Junji stay in her home was because "misery loves company".
Doyeon loneliness comes from being apathetic and, without even realising, she set up a facade of good, selfless and calm person so people would like her, and she believed her own lie, although it's tiring living like that.
Junji must have been her first desire and I do believe she loves her, but the whole situation with her would be stressful and frustrating for anyone, and since she is not used to strong feelings, when she snaps, it all comes out mixed as desperate, glorious sex pages for us degenerates to enjoy.
I don't think Junji is manipulative. Her parents abandoned her, her husband abandoned her, she has every reason to not trust Doyeon's feelings. So she pushes Doyeon away out of mistrust and guilt, but doesn't leave and seek shelter somewhere else safer, because without Doyeon, the only person who at the time cares for her, she would be alone again, so she ends up giving in to Doyeon (I mean... who wouldn't?).