Yep, that was ep 4. I saw that and thought, ah, ok, he wants Hira to be his own private slave boy and can't stand that Hira's moved on. I thought Kiyoi needed a comeuppance after the way he treated Hira in high school, so I LOVED that he was jealous. Indeed, I replayed this scene a half dozen times when it aired. The way he darts his eyes!
Then, in the same ep, he revealed that he tried to call Hira but Hira changed his number. That's when I thought, humm, this is getting interesting. Nevertheless, I hadn't realized that Kiyoi truly loved Hira deeply until ep 5. In that ep we see this same scene with Kiyoi doing another great expression with his eyes when he thought he had won over Koyoma. Remember that "victory glance" Kiyoi gave Koyoma? I replayed that a dozen times too! lol. That actor was so great at expressing emotion with his eyes.