Not to mention not stating that it’s possibly not his and possibly putting him in a situation where he has to sign a document that states it is. Cheating is possibly forgivable. This needs to be a fucking criminal offense. You just summed it up perfectly. Cheating can not and should not be made into just a “mistake”.
The way you’re dealing with this with a level head is commendable and that child is very lucky to have you. Many people wouldn’t respond how well you are and you deserve a ton of credit for that. Your life was thrown upside down and you’re still putting the baby’s best interest first.