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It was fine.
He enjoys talking about it. I know that may sound weird, but it's how he is. Talking about it, joking about it, and explaining it in detail demystifies it for him. So all I had to do was remain composed when he compared and contrasted radiation and surgery, told me his and his wife's rate of intercourse (twice a month) and that, because of the meds he's on, he no longer ejaculates.
The cosmo helped.
I promised him we'd do this again before his surgery next month. I'll be more used to it each time we meet.