Notre Dame Des Fleurs - and her hypnotic gaze

[Hanahaki Disease]
Tony Stark did not exactly know when it all started.
Maybe, something sprang the moment he saw Stephen again and alive by his side in the chaos of the battlefield, or maybe even before, the second he believed that it had been indeed the Sorcerer who slapped his ass, back then in the Sanctum.
It was also possible that the thing for Strange happened much later, the day Tony finally decided to go and meet him.