@UndaT no its more like, he's holding himself back because he respect Karen and doesn't want to do those things easily. in my opinion and how i see Mii-kun, he's a rational and quite just in decisions making, he wants to be stable before marriage, he didn't want to leave his mother because his father is still in another region working etc. because if he does what Karen's to-do list he will lose control of that rationality, which he doesn't want to, i think he prefers to take their own time since Karen is super duper shy after their first kiss and he wants to see Karen have her own fun in their age.
in this one, he was basically still having that kind of wall, i mean because he's jealous ugly thoughts reared up in his mind, like "why i didn't became more possesive more clingy more protective eventhough she's mine/my girl," but he keep denying himself those ugly thoughts, so yeah in the heat of the moment he thinks like that. and also maybe because of Jp shoujo trope or mindset, but the more showy you are about the relationship/with your lovers, it will kinda fend off the other competitors? lmao idk its just what im seeing often on manga
jesus wall of text sorry