My husband told me early on that when he was in college (back in the early 90s), he and a bunch of his fraternity brothers went to a sperm bank to donate their sperm for the cash. Only a few of them were accepted to donate (my husband was one of them). He claims that he was told his sperm was just a number and it would be completely private with the receiver having no way to contact the donor.
I'm 100% OK with his past, and even if someone showed up today claiming to be his child, I would be ok with it. I'm not sure how I would feel if it wasn't so far in his past and if it wasn't a fraternity "outing" - but I wonder, would you be ok if your SO donated his sperm previously?