Despite how slowly he and Miharu were taking things, he more or less committed to wanting to be more than friends, eventually.
Then, right after a date with Miharu, he starts going out with a girl they're both friends with. It's awkward and shows that his intent toward Miharu wasn't as serious as he made it seem.
And sure, you can definitely make the argument that love is complicated and feelings change, that's fair. But we're talking about a dude with no social skills who needed a therapist to tell him to sleep properly. And no disrespect to anyone taking therapy, but ask yourself if you think this man, in his current state, can pull off a clean breakup and everything that would follow.