I know this is an old thread, but I watched this a few years ago and this was the second time I have watched it. The main reason for the second season I think besides the bad-rep for "sex" is that the manga doesn't go past the end of the anime, so there's nothing to build on. Plus, how much farther could they have gone with it in the first place?
***And Spoiler Alert:
If you read the manga, there is a lot more detail and interaction. It's all the same story but it isn't told so fast.
Also, when they go to the hotel, there is a lot more detail on what they do as well as the fact that they actually do have sex. As much as I know they could've done a better job with working with the original material from the manga, the manga is actually very graphic compared to this. It's still censored a bit, but in general, they imply more things than in the anime.
The anime kind of failed because it didn't fulfill it's purpose of them actually doing it, which I think they could've really pulled off well, even if it meant adding a couple more episodes.
On the other hand, the manga was great and had a lot of detail, but I think that it doesn't have the same funny and "teenage" feel to it as the anime does. I think that somewhere in the middle would've been great.