Not the person you're asking but he's unworthy for lying. It's either lying outright or lying by omission. It's his body and his to do with what he wants. If donating his sperm to a friend is what he wants I would be fine with it, but it would be the end of our relationship. It is also about who it is with. It is with someone that causes stress on their relationship. He didn't tell her because he knew it would be a problem.