Would you stand for someone in a wedding you don't agree with? [View all]

[Xithras]

The shortish version in a long and sordid story: I've been friends with a guy since college, and he recently asked me to stand for him as a groomsman in his upcoming wedding.

He's a 44 year old divorcee with a 19 year old daughter. Earlier this summer, his daughter and a few of her friends were drinking it up around his house (he says he was drinking too, but not WITH them), he ended up in the hot tub with one of his daughters 18 year old friends, one thing led to another, and two months later the girl is apparently pregnant with his kid (it only happened once, but there are various reasons that they're sure it's his kid).

The young woman is apparently from a fairly fundy family, and they're now insisting that he marry her...in spite of the fact that he's virtually the same age as her father. I suspect that his relative wealth factored into their decision a bit (he's not super rich, but he's accrued a couple million over the years and is pretty well off). He didn't have a problem with marrying her (can't imagine why), and they're tying the knot in 3 weeks.

His daughter has disowned him over it, as have a number of his friends. I personally don't have a huge problem with the sex part (44 and 18 is a terrible idea, but I tend to take a "willing and consensual adults" attitude toward most things and won't condemn him over it), though I do think he crossed a HUGE line when he did it with a friend of his own daughter. There's also a difference between sex and marriage, IMO, and taking the "relationship" to the next level like this is an absolute mistake and should end spectacularly (bye bye wealth!)

Here's the thing. If I say no, it will probably be the end of our friendship. Other than this one thing, he's normally a great guy and we've been good friends for years. He and I have literally climbed mountains together, and have spent untold months in the wilderness, covering hundreds of miles, hiking the Sierra backcountry over the years. He's been a good friend, and I don't know that I want to write that off over his new bride. But if I say yes, it might give the impression that I support the marriage, which I 100% do not. I think it will ultimately ruin both of their lives, and have already said as much.

What would you do? What would you say to him?