Wait up! They're simply roommates, right? Yuiko's in love with Mei, while the latter is tooooo dense to notice it. That was why Mei thought Yuiko might simply be doing some kind of training for when she gets married to some one else (not her) in the future. Anyway, that's some really nice art.
Yeah Mei is obviously oblivious to Yuiko's interest.
That's why Yuiko hints at the end that she wants a special wedding dress.
I can't see this ending well for them, tbh, even if Yuiko confessed to her.