I think he has a right to be open about his past partners IF he wants to, but this is his decision... he's the one marrying this woman. He should not ask you to make this decision.

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Put me on wheels and I'll turn tricks.

Clever? Nah, I ran out of that years ago. But if you find this, let me know, k?
"The road goes ever on..." ~ Tolkien

In memory of my friend skip...
Go then, there are other worlds than these