I agree with Dan. It IS a big decision, often a life-changing one. I was not willing to risk being with another guy until I was confident 100% that my marriage was solid at its base. For me, since hubby was the first guy I was ever with, it was really to explore and see what I had missed in my younger days. I think a lot of it depends on how solid the marriage is, and why the woman wants to do it.
Good luck to you both.