He and I have already discussed this topic hypothetically because it is something that can happen even in the best marriage. USA I am in agreement with Beverly from Alabama in that I'd only tell if I was asked. I figure that if my spouse could tell enough to ask the question, then I'd already given away the goods in latent guilt. If not asked, then I'd not tell. As to STD problem.
Fact is it is difficult as hell to catch most STDs.
I'd get myself tested at the appropriate delay after the indescretion. A spouse would be hurt in the process and they have done nothing wrong. I feel that a person would be telling a spouse in order to relieve their own conscience and that is not a reason to tell someone something that would devastate them. It wouldn't benefit anyone if you disclosed your indiscretion. Allow yourself the freedom to be an indiviual for one moment again.