Maybe put it in a non-threatening way, like "you know, it always made me sad that I never got the chance to model for your photography." There was a psychiatrist who like to phrase things can you "help me understand". Maybe, "can you help me understand why the time was never right". Even if he gives a lame response, he will think about it and maybe later give a deeper answer. At least he will have to think about it.
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Impermanence.