He wasn't answering your messages. you both were really close friends who told each other everything. One night you needed to talk to him about something but he wasn't answering. You decided to visit his house. You arrived and knocked on his front door, when he didn't answer you took the spare key he gave you and opened the door. You walked inside slowly and walked up to his room. You knocked again and you heard him say

"Come in."

You walked in and there he was. comforting a girl he didn't even know that well. the girl he's replaced you with. You looked at the two before apologizing and walking back out of his house. he tried to stop you but the girl told him to stay. and he listened, of course.