OP... I agree with EVERY word that nickymanchester has posted and, for that reason, think very, very carefully about whether joint counselling is the right thing for you. I would never use a counselling session to 'confess', it would just seem even more cowardly to me. That's just my opinion though, there's certainly something to be said for perhaps having a third party around as a support to your husband following your revelation.
The affair is down to you, this whole thing is down to you as far as your marriage goes. What you say cannot be 'unsaid' Do you want to disclose the affair knowing that it could end your marriage? That's the question and it's YOUR decision to make because you are the one that will live with the consequences of that particular decision, irrespective of the pain you will cause your husband.
I think, if you are determined that you will end your marriage anyway then honesty might be the tool that will set you free from subsequent guilt, or at least get you on the road to recovery.
If you think that you could repair your marriage, take whatever steps are necessary to do so and put in the time and effort, then disclosure may not be the right thing for you. If you decide on non-disclosure then this secret goes with you to the grave and you have your work cut out to 'cover up'.
Make no hasty decisions, take the time to work out what you will do next and how you will go about it. Think it through.
I'm sorry for your pain, Duck, I really am. It's a horrible situation and, just because you put yourself in it, that doesn't take away what you are feeling now. Nobody ever sees themselves at the 'end of the affair' when they're embarking on it. If they did, they never would. :(