they expect him to pick at some point.
They say this, but I don't think they really want it to happen--I take it as their simply not considering the possibility of a stable three-person relationship.* Neither of them want MC to pick the other one, but they also don't want him to pick them and send the other one away. To use one example, Tina loves MC, she sees that Robin loves MC, she sees that MC loves both of them, she loves Robin, Robin loves Tina. Swap "Robin" and "Tina" there, or put in Anita and Marisa, and it's just as correct. To the extent they want MC to ever (but not now) choose one of them, I think it's driven by the convention (enforced by the pre-DC endings) that MC can only be with one of them long-term.
two characters (seemingly) not getting an ending
I'm pretty sure there's an ending for each (female) character (nope, no ending for Edd). If you interact with her, there's an ending with her; if not, she's a shade. Unless I'm forgetting one? Edit: Mina, maybe? There is an ending with her, but it requires what might be a non-obvious choice in her story.
how low qi i somehow have this late into the game lol.
The path to seeing the most content in TID is to advance the characters' stories pretty uniformly. Your primary source of Qi is sending them on, which naturally happens at the end of their stories. Put those two things together, and you're going to go a long time with very little Qi (and even have to spend a bit of it for the best outcome), and then get a lot of it very quickly.
* And they aren't aware MC's with a dozen or so others at the same time. Tina knows the most--in addition to Robin, she knows MC's with Kaitlin and Anya--but none of them know everyone else he's with. So while they say, "you'll need to pick between Tina and Robin at some point," unbeknownst to them, MC's playing a much larger field. I don't think MC is at all being an "asshole fuckboi" to have a relationship with both Anita and Marisa at the same time--both know about it, they're both fine with it (once Marisa gets over her competitive streak and body-image issues), each knows and loves the other. The dozen others at the same time he isn't telling them about? Well...