Funny thread.
It's tough to pick just one. I heard:

Relax. Someday we'll look back at this time and laugh that we ever had to go through this.

She's done nothing wrong, so I can't hurt her.

It's not healthy for us to share a bed anymore, because I won't have sex with two women.

And my favorite:
Having my own child has become very important to me. So I'm better off with a younger woman who isn't running out of time, because there's less likelihood that I will have to pay for assisted fertility.

I could go on.... but I'll stop here. Looks like we all hear similiar statements.