AITJ for not telling my roommate that I found his cat before he spent three days looking for her?

Okay I know how this sounds. Let me explain. I live with two roommates, Marcus and Dev. Marcus has a cat named Pita who is an indoor cat and is not supposed to leave the apartment. Three weeks ago Pita got out somehow, probably when Dev left the door open unloading groceries, and Marcus spent three days genuinely distressed, posting in the building group chat, putting up notices in the lobby, the whole thing. Here's the part I need to explain. I found Pita on day one. She had gotten into the storage unit in the basement that we share access to, probably through a gap in the dropped ceiling that connects to the utility space. She was fine, had access to a dripping pipe for water, was just sitting on a box looking annoyed. Here is why I did not immediately tell Marcus. Marcus had two weeks before this told my girlfriend directly that he thought she spent too much time at our apartment and that it was starting to feel like she lived there. He said this to her face without talking to me first. It was a whole thing. My girlfriend was upset, I was upset, and Marcus apologized but only sort of, the kind of apology that explains why you were right to say it. I was still genuinely angry about it when Pita went missing. So I visited Pita twice a day, made sure she had water, left some food, and did not mention it. On day three I "found" her during a very visible search of the basement while Marcus was with me. He was so relieved he cried a little. I have not told him the full version of events. My girlfriend knows. She thinks I should tell him. Am I the jerk?