A former mistress (26 years, on-and-off) describes the good, the bad, and the ugly of her long-term affair. Conclusion: Affairs aren't necessarily destructive if kept in the correct perspective. Our experience enhanced BOTH our marriages.
That is, until his marriage ended and we began to love each other. When the affair morphed into a relationship, well, that's when it stopped being fun for me.
For 26 yrs we luxuriated in implicit Trust. When B. cheated on ME, it was the first time another person came into our relationship besides our respective spouses.
We have now irrevocably split.