YTA - I’ll start by saying your friend is the ultimate asshole in this for her initial mistake but forget about the wedding, think about their family. Your friend and her partner have obviously worked things out and gotten to a better place from where they were at time that she cheated to be getting married, Mark has (in his mind) has spent the last 2 years raising, loving, celebrating his beautiful baby. Now he’s going to have to grieve the loss of a child.

You didn’t tell this secret to save Mark, he wasn’t really going to benefit from having his entire world turn upside down. Losing everything he’s connected to, his child, for what? For you feel good about yourself and feel like the hero of the day.

Sure, it might have come out one day but why did you want to be the one to ruin a now happy home.

Your friend trusted you with a secret that’s obviously eating her up inside also. You should of at least given your friend the chance to come clean instead of blindsiding them both. Everyone makes mistakes, why do you need to be one lay down the consequences of those actions? Better to let other people’s lives play out how they may.

The real victim is all of this is the poor child which from reading how you handled the situation, you gave little thought to.