Sue,
Welcome to this board.
I think it´s best to deal with guilt by not doing to much about it. You have a disease and you are dealing with it, so leave your mistake in the past where it belongs. I assume you have done all the right things, gone to have tests to make sure you and your husband will be OK.
You will find that guilt, like everything else, gets better with time. Talking about it, moderately, with someone on a help line or post here will help to a degree, but eventually the work is within you. You´re working hard to make your marriage work and that should lessen the guilt.
You could also use the energy the guilt takes by doing some project or doing exercises, meditation or yoga. You can use self-talk to strenghten you. Just remember, you made a mistake, you have learned from it and the only thing you can do about it is that you will not repeat it again by drinking or using drugs.
Good luck.