It would mentally destroy Chisaki if she finds out they actually went to the love hotel and go all the way. Tsubami was seconds from taking Ueno's virginity the last time they were together.
Tsubomi is the easiest girl out of the trio for Ueno to resist due to how easy for her to get embarrassed. Hoping Ueno use that to his advantage later to tease her, lol.
Taking her out to eat her favorite meal and noticing that she cut her bangs? Ueno, keep it up, man.
Bad luck for him to run into Tsubomi at her job, but she's overdue for some content anyway. It's nice for Ueno to try to shoo Tsubomi away even though it didn't work out in the end. Looks like Tsubomi is going to continue her intimacy training with Ueno so let's see if she's actually going to suck him off without freaking out.