If you have been with a partner for 20 years and find out that he had a child and hid it from you for 9 years what should you do?
You should talk. A lot.
Did he tell you or did you find out on your own? Have you talked about it? Not fought about it, but actually talked about it as calmly as possible. I realize this must come as a shock and you are probably feeling a lot of things including anger and frustration. But understanding the situation better will help you put things in perspective. Why did he hide it from you? What does he expect to happen now? What do you want to happen now?
It’s a complex and crummy situation but it doesn’t necessarily mean you can’t find a way to work through it (assuming that that’s what you want). You need to be able to hear his story and to have him hear how this has made you feel without it disintegrating into an argument. Is that possible? If its hard to do this on your own right now, think about seeing a counselor who can serve an a mediator as you two work things out to some resolution.
I wish I could tell you there is some easy answer but relationships never provide us with easy and they often provide us with downright difficult and disastrous. If you love your partner and you want to be with him, then you’re going to have to work on acceptance and forgiveness. Work on rebuilding trust. Sometimes things happen and we can’t take them back or control them, but you have choices. You can choose to let this relationship go despite the many years you’ve been together. Or you can choose to acknowledge that what your partner did was crappy, that hiding it from you added insult to injury, but that it is possible to move forward together. It’s just going to take some work. Most of all, you need to take care of yourself and your emotional well-being. You didn’t ask for this and though you might wish it never happened, you can choose to become stronger and self-aware as a result.
Don't be shy! Say what's on your mind and get a good dose of perspective in return.