I may be in the minority here but I do not think what he did is necessarily relationship ending- if its the only thing and only time ever concealment or omission or lying popped up. If he is not in the child's life ever- as in no child support, no visitation, no communication, hasnt seen the child in years-then I can see where he might be ashamed and think you would hate him or think he is a bad father and not tell you. Its still not ok- but its something I think you can recover from.
If however he has been paying support all this time or knows how the child is doing or has any sort of communication with the baby mama or anything current then I think its a problem. I feel this way because being constantly reminded of a child by paying support or having info shared with you by an ex or any sort of currant info is not something you can forget about or not tell your current partner about. Its flat out deceit. Its calculated and its on purpose. But if its nearly an after thought because he really has no idea what is going on I think its something that can be worked through.
Did he sign away his parental rights?