Well, this chapter confirmed that Sakurako isn't the one who gave Yuhi her necklace. My current read on the the plot is that Yuhi dated some other girl in the past who gave her that necklace, but things ended very badly, so Yuhi gave up on love similar to how Sakurako has. Then, Yuhi just started having casual flings. The story is likely Sakurako/Mocchi helping Yuhi getting over her heartbreak, thus allowing her to form a meaningful relationship again, as symbolized by Sakurako's collar replacing the ex's necklace.
I'm also not 100% sold that Saki didn't notice them together. Would spice up the plot for her to be interested in Sakurako and try to make a move now that she knows Sakurako is into girls. Could also give Yuhi something to think about, either get serious, or Sakurako could dump her for her friend.