Yeah, I have read the source, so I am only going to talk about what we have seen up to now. The anime is ahead of the manga at this point, and characters can change over time. Makoto is about as late a bloomer as you can get. He gets flustered any time he sees some exposed skin or a woman makes an advance on him (the brothel, the medusa, Hibiki’s new outfit, the students that propose to him). In the past he had even blasted Mio and Tomoe with magic to escape them as they made an advance. So, his kind of fumbling around about what to say to Mio this time is a tamer reaction than we have seen from him in the past at least.

As a side point though, I do understand not being able to see past the fact that the person you are considering becoming intimate with was at one point a giant spider that came close to killing you. That would be traumatic. It certainly was for Hibiki’s party. However, an “invincible” dragon that proved to not really be a threat? Where do I sign up?