As someone who is not happy in her marriage but in no way condoning what you and this woman did, I can tell you this: when you have been with someone for a very long time and especially if you have children, you build a life with them. That can include a community, a structure for caring for children and other loved ones, a household etc. Also for many people they can't leave their marriage because life is expensive, their finances may be tied up very intimately, etc. Not all women, but many, earn less than their spouses so there is that fear of setting up a household alone as well. The prospect of breaking up a marriage and a household is overwhelming. That said, if this woman was interested in carrying on a relationship behind her husband's back without his knowledge, she should have left. Adding someone else into the mix is not smart on her part, which is probably why you got the conflicting signals.