I feel Guilty.....what do i do?

Tell the mistress you feel really guilty and cant meet with her again, and really sell it so she doesn't get mad and think your not into her or the was bad. Hold off on telling your wife, youre in shock now. When you get back make an appointment with a psychologist and discuss your guilt with them (no one else, tell no one else.) Decide at a later time whether to tell wife or not.