Mizushima-kun has awoken. But he is still a novice yuri danshi. A veteran does not interact with the couple, he just observes the lilys bloom from a safe distance. But he has to help in this case, its understandable. He will learn one day though.
Happy that he jumped in and told her what she needed to hear(should've said some more). She is too aggressive and again it comes off as very creepy, controlling and toxic.