Aoi looking like Mashiro makes her being one of Amano's "playmates" makes a lot of sense.
Mashiro being an adult while Amano(Yuhi) is still a student goes a fair ways in explaining why Yuhi is the way she is. Age gap romance is not uncommon in yuri stories, and is being coded as a "not-good" thing here. Yuhi being exploited when she was younger by an older Mashiro and "used" in some way would explain why Yuhi is the way she is now. And, potentially, why she was the way she was when Sakurako first tried to confess to her.
Honestly, I'm betting Yuhi even would have gone with Sakurako back then, but Mashiro had some hold over her at the time (ether by being in her life, or by screwing her up and then dropping her, leaving Yuhi all sorts of messed up), and it's only gotten worse since then.
The fact that Mashiro is showing up again, when Yuhi's older(?) sister is home, could mean that Mashiro was always involved with Onee-san, and went after Young Yuhi in secret. Which makes it all the worse, and could further contribute to Yuhi's messed up view of relationships and sex and love.
But, betting Yuhi is very much hung up on Mashiro. She welcomed Sakurako's "pet play" so readily that it's pretty clear she's had some history in power dynamic abuse, and Mashiro is looking to be the genesis point of all of her troubles.
So from here....Sakurako unfortunately has her own things to sort out, but if there's any hope for Yuhi and for a future for the two of them together, she'll need to be proactive in forcing Yuhi to explain and reveal her secrets.
The question will be, how that plays out.
Thanks for the TL. Glad this one's still going.