While Saki and Nodoka kept dancing around each other, these two were practically Married.
Best scene is from the Achiga Side A spin-off anime, where the Achiga girls run into Momo and Kanbara and head to Kanbara's house to train with the Tsuruga Academy girls. When they arrive, Momo just glomps Yumi right there in front of everybody.
There's also the implied sex scene in the hot springs episode of Saki. Yumi is sitting by herself in the onsen and she's pretty close to an O-face. The other girls arrive and then Momo appears out of nowhere. With the clear hint that she was putting her invisibility powers to good use until other folks started showing up.
