Forgive me. I've just read the first released story to better grasp this current released. First, my vocabulary is a little bit messed up on "prequel" tag. The way I understand it, this current story is an insertion of the first released. Consequently, I considered these points:
1.Shiori is a closet lesbian. She is physically attracted to Touko. Her parents let her do what she wants but strict on to whom she closely associates with. To which, I assumed the family practices on "arranged marriage".
2. In the course of time, both fell in love. It just happened. Both didn't realize as this was not their original intention.
3. It was Shiori who made a move to live together. Reason? She longs for that physical contact.
4. Touko is emotionally expressive, a Top-partner with a compulsion on tantric sex. lazy, no-drive for bettering herself, stress-free individual.
5. Shiori is not expressive verbally but can easily be read to which Touko can't since she is dense. Shiori is "reputation" conscious which I assumed because of the family. In sex, she is a bottom who likes to be on top.
6. I emphasized on the sex because I believed this is where they connect. They are just sexually compatible. For in communication, they amissed.
7. The brokenness of Touko comes from an innate desire on the "forever" to which Shiori knew all along that it is impossible.
For me, it is beyond cruelty to lead a person. To let them believe, invest emotionally(time, effort, dreams) for nothing. It is like for me robbing them of their humanity. It is insanely degrading. I go for a goosebumped clichè, "Honesty is the best policy", but... still works.