I'm not a Stan fan, but I am an advocate of the devil, so I will disagree here. This scenario you presented, and so far as been the case if Lena threads the needle well enough, can absolutely be the beginning of a good relationship. There can be a strong foundation of empathy between the two characters, and that level of understanding is how friendships and kinship are born.
It will require a good deal of additional writting from EK to properly complete that arc. And more importantly it will take a good deal of players understanding what is going on to not have it devolve into Stan becoming a simp or incel or otherwise creepy dude. So far in my experiences with Stan, respecting his boundaries as a character, and he will respect Lena's. i.e. don't tease Stan during the photoshoot with him, scold him appropriately about his room and him masturbating to Lena, but don't side with Louise on every little attack on him. Do that and there is seemingly a solid friendship forming between the two characters. The key to Stan, and I know this will sound boring, is a lot of neutrality with your choices.
This is a case where I'm disappointed Louise disappears for awhile, but I suppose it's to better setup Stan and Lena growing their relationship, but I want to see the misunderstanding between her and Stan be mended as well. I don't think they necessarily need to start dating, I don't think that would be healthy for either of them no matter the level of writting. However, the two of them burying the hatchet and learning enough about the other to understand the boundaries they have would make for a wholesome arc on that front of Lena's life.
