@givemersspls
I'll tell you what happened, but I can barely call this a spoiler.
The couple never kissed. They hardly told anyone about their relationship. Urabe's parents are never seen. We never really find out anything about the drool bond. At the end, the girl asks to be kissed, but the guy stops her in order to continue the drool-licking thing. That's it. The strange status quo is upheld. They stay 17 forever.
It's still one of my favorite manga, but it's 12 volumes of journey but no destination. I like the art, and I like Urabe, and I like seeing their bond strengthen over time, without sex or even kissing. I thought that was pretty romantic. Still would've liked it to end with a "5 years later" chapter.