In Harry's third year when Sirius had escaped Azkaban and had his name cleared he went to live with Sirius and Remus. Harry loved this for a while until the first time he walked in on some things he could live without seeing.
Harry was sitting in his room and decided to go and get something for lunch, he went to ask Sirius and Remus if they wanted anything knowing now this was a bad idea. He knocked on the door (there was a silencing charm up but he didn't realize) and got no answer he knocked again and with no answer he decided to open the door. When the door swung open he looked up and saw why they didn't answer. Sirius was lying on the bed, arms tied above his head moaning Remus’ name. Harry walked out and went to get food and never mention this ever again.
The next time Harry walked in on them was partly his own fault, he was staying at the burrow with Ron and Hermione for a few days when he decided to go home early; this was his first mistake. His next mistake was that he didn't think about the fact that Sirius and Remus thought they had another few hours alone. He used the floo to get home and when he landed in the living room he walked upstairs to put his bag away. He went to find Sirius and Remus (again they had a silencing charm up) he opened the door forgetting to knock, when he opened the door he saw both Sirius and Remus with no clothes on and Sirius sitting on top of Remus he walked away and tried to act like it never happened and get that image out his memory. (it didn't work)
The next time he went to bed and was trying to sleep, Sirius and Remus forgot a silencing charm and he could hear everything. The next morning he got up and went downstairs for breakfast acting like nothing happened, he sat down to eat like normal, Sirius and Remus sat across from him like normal. He finished eating and looked up at the men in front of him. “By the way, I think you should practice silencing charms. Sirius is loud.” They both choked on the food they were eating. Looking up, Remus asked “what? When?” Sirius was still sitting in shock. “Last night if i can remember them i think you can too.” “What do you mean you remember? Are you seeing someone?” Sirius asked. “Yes, I'm dating someone.” Harry replied calmly “who?” Remus asked him “Draco Malfoy” harry replied turning to walk away leaving them speechless. He thinks he heard a loud WHAT from Sirius as he walked away.