I bet that when Ron and Hermione FINALLY kissed harry acted cool on the outside but on the inside totally fangirled. After the battle he waited until all was quiet in the Gryffindor common room...and began squealing like a perfect fangirl. "OMG OTP OMG OTP OMGOMGOMG!!"
“I love you, Hermione,” said Ron, sinking back, rubbing his eyes wearily. Hermione turned faintly pink, but merely said, “Don’t let Lavender hear you saying that.” “I won’t,” said Ron into his hands. “Or maybe I will … then she’ll ditch me …”
The reason I don’t believe that it was their 1st kiss was that they were practically an item even at the wedding, and I don’t think they spent 9 months in close quarters without ever moving forward in their relationship. I think it’s far more likely that they were moving slowly and keeping it on the DL because they didn’t want to hurt or distract Harry. - part 1