Tony had learned, over and over, that caring about others was a mistake. He had cared about what his father thought of him, and his father had never spared him any time. He had cared about Jarvis, and Jarvis had died in a car accident when Tony was still a teenager. He had cared about Obadiah, and Tony had been tortured in a cave for three months and had his arc reactor ripped out of his chest. Caring was not a safe or healthy decision.
Then again, Tony had never met a bad decision he didn't like. Maybe that was why he allowed Pepper to slip past his defenses again and again. Why he had started relying on and trusting the Avengers. Why he had started spending his time working in the lab with Bruce, joking with Clint, chatting with (despite still being a bit afraid of) Natasha, and bickering with Steve. It was starting to feel like he had a family again.
And even though he knew that it wouldn't last and was waiting for it all to go wrong, he couldn't bring himself to stop caring. It was stupid and reckless, and it was exactly how he rolled.