I wrote this as a quick fluff shot with minor cannon sprawled in there.
After Harry was let out the hospital wing in third year he headed to the Quitdtich pitch to attempt to stake a claim on one of the school brooms. As Harry made his way through the halls however, a tall figure creeped up behind him. The figure tapped Harry on the shoulder, making him jump out of his skin. The figure laughed, and Harry noticed it was the Hufflepuff seeker, Cedric Diggory. Harry smiled at him, and they began to talk, with Cedric walking Harry to the Quiddich pitch, eventually the conversation leading to the topic of relationships. Harry thought Cedric was dating Cho, but as explained by Cedric with a laugh, he was way off base, and Cho and he were just friends. Harry couldn't comprehend why, and began to ask, when Cedric gave him his answer through a kiss. Harry gasped, experiencing his first kiss was amazing. He closed his eyes and leaned in, Cedric holding him tightly. It was magical.
Sadly, Cedric eventually had to let him go, but Harry felt the need to ask what that was about. Cedric responded with a simple claim of wanting to, and then asked Harry if he would like to date him. Harry nodded shyly. Then Cedric grabbed a hold of Harry's hand and they walked out to the pitch together. No one else was outside, but if someone happened to look out a window they would have seen the two boys kiss, hug, and race each-other for the snitch, each getting it at different points in their game.
Once they finished with their game, the boys walked back into the locker rooms to change. Harry hid from Cedric, embarrassed now that they were dating, and Cedric respected this. Once they were finished they walked back into the castle holding hands. Cedric walked Harry to Gryffindor tower, and gave him a kiss just as the portrait opened to reveal Hermione. The boys were in shock as was Hermione.
Cedric smiled sheepishly, while Harry got red in the face and tried to explain. Hermione laughed at Harry's attempt to explain, and just said to "be safe" in a very provocative manner, causing both Harry and Cedric to turn an even worse shade of scarlet, matching with Harry's Gryffindor colors. Hermione left them and they hugged and Harry stated the password, waving goodbye to Cedric.