It wasn't sappy at all. It was very sweet. Teenagers are loaded with self-doubt, especially teenagers who had been abused or shunned most of their lives. Harry and Hermione had been through the mill up to this point, what with childhood insecurities and all the crap they had to take about Rita's articles.
The raw honesty in this chapter made it the success it is. And yes, good fluff is very hard to write, and sex is even harder (no pun intended). Love scenes of any kind can be either sweet and romantic or shallow and sophomoric. You hit sweet and romantic right on the head here. Well done!
Indeed, I think the lives Harry and Hermione had led up to this point made their self-doubt believable.
Glad you liked it. I think your review was more eloquent than the story itself is. :)