Jo and kailope: thank you for the suggestions. Those are helpful. One of my concerns is finding the "right" counselor or support person. I'm afraid that issues of sex and cheating will be hard for that person to dissect and counsel in a somewhat supportive way. That's probably because I already feel guilty myself but also, counselors are people too and have their limitations and biases.
Recommendations would be great but I don't exactly want to ask my friends if they know of someone who deals well with these issues.