I am so sorry to have to welcome you here. But, you have come to the right place. What you are going through now is the worst you are going to feel so now there is nowhere to go but up. You'll find a lot of advice, support and comfort here.
First of all, you are experiencing the worst possible thing that can happen to a marriage. And affair is bad enough, but to include an OC into the mix "squares" the pain. There is nothing worse. Nothing.
The stages you will experience over the next year will be confusing because you will go from profound grief to outrage to denial and back again. The stages will shift around and until you get through the grieving part of it and settle into a kind of acceptance where you will be able to think more clearly and finally make some decisions.
The first thing you need to do is begin by reading everything you can on this site, starting with
The General Welcome for New Builders Lots of VERY useful information and links there to help you understand this site and the advice you will receive on the forums. On this thread you will also find the links for Plan A. Learn the Harley very effective principles and methods for marital and personal recovery. If your H is sincere and determined to make this marriage work, he should begin reading all the material available to rebuild the marriage. Whether or not he participates in this program of recovery, it is important for you to do so just for your own personal recovery from this devastating blow.
If you decide the marriage is worth saving and that you are willing to do what is necessary to rebuild, then learning the Harley Principles is the best place to start. There is an Emotional Needs Questionaire that you and your H should fill out and then discuss together. Some strongly suggest you both get into marital counseling with a pro-marriage counselor, preferably someone familiar with the Harley Principles (because these policies really work). Phone counseling is available on this site with the Harleys.
The Rules of Radical Honesty and Rules of Protection along with the Policy for Joint Agreement will help your marriage recovery.
While you are in so much turmoil, you should not make any drastic decisions about anything. Let everything settle down for a while and after you feel you have calmed down enough to think clearly, you can consider some options.
The hardest thing is the disappointment and confusion over the Betrayal. The shock that someone you love so much is capable of doing something so horrible is something you'll never be able to shake completely. It will get easier in time. I know it is hard to imagine now that there will ever come a time where you won't be in agonizing over all this, but you will get through this even if you decide to stay in the marriage as long as your H works the recovery. This is a time for you and your H to re-connect, to talk openly and honestly about what has happened and why it happened, and then to make every effort to re-build your marriage. This is a time for the two of you to concentrate on each other and to find out where your hearts are truly telling you to go.
It is heartbreaking to know that so many women and men share this problem, but at the same time, it gives you hope that recovery is possible. You will learn to laugh again, love with your whole heart again, and trust again. But, it will take time and effort . If your H is committed to making the marriage the safe place for you both that it once was, you can move forward.
There are wonderful and caring people on this site. Keep posting and draw from the wisdom and strength of those who have been through this and survived it, and those that are travelling that same road with you. Just know you are not alone and that recovery is possible and that you won't always feel this horrible. It will get better.