Because that seems to be everyone's complaint:
It's been spelled out a few times now in later chapters. Obviously, she won't kiss him because she's nervous, which is normal. The reason he won't kiss her is because he wants her. Badly. As he's explicitly said, he's afraid if he lets himself go even that far, he won't be able to resist going even further, so he's playing it safe. In other words, it's part of the jailbait wait.
Oh, also irony. x3 Because the entire slowly-updating pretty lengthy manga is LITERALLY still faster than their kiss. 😛
As to my personal opinion of the series, I admit it can get a little tedious at times, and all the filler can in a few places seem somewhat repetitive. However, it's still rather filled with win. Teppei is cute of course, but I've never really gotten the level of rabid fandom; personally, aside from the main duo, I'm all about Ryuu~ x3 He makes me laugh so hard.
I don't really see it as a harem, because only one other guy really wants her, and really- what kind of student-teacher romance would it be if there wasn't a single student competitor? The other who kind of seems to has his own girl clearly designated already, and otherwise he (and everyone else entirely) is more straight conflict than competition. Anyone who's ever really been in a serious, long-term relationship should recognize that the appeal of other guys or girls, especially once tied down, is very real; but being able to overcome that desire allows one to find all the more to love in one's partner.
All in all, I think the series is rather well-done with more than enough good points to outweigh the bad completely. The characters are lovable, and while I'm sure they have clones in some series like just about any characters I haven't seen them, so at least to me most seem unique. Character development is slow but believably so and certainly well-done in the long run. The art is beautiful, and the story is both touching and hysterical. The utterly random spaz moments are what really drive it home for me (such as a horned Kazuma popping Fumino's fricking thought bubble with a pitchfork), and I never cease to be surprised just how much they can make me laugh.
The only actual issue I have is the update times, but all things considered it's worth the wait.
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