This could hurt people. The secret stuff is the destroyer of partnerships - you split into another life when you hide a part of your life from your partner. I learned I am capable of loving more than one person, but that I can't live that way. I also learned that there were things in my marriage that I needed badly and didn't know it till I experienced them elsewhere. All of this was learning and it helped my marriage in the long run.
Sexual affairs are sexual affairs are sexual affairs.
I guess it's safer than having a physical affair in some ways. I can still say I've only slept with one man. But I have certainly been made love to by others. I would have maybe had a physical affair without it. It's another chance to learn about oneself in relationships with others.