This is what Dr Harley says...
Dr Harley's response to affairiage they are warning you about what happens to relationship that originated as an affair. I have counseled hundreds of these couples and am presently counseling couples that married after an affair, and I can tell you from first-hand experience, and their own unsolicited comments, that if they had put the same effort into their marriages, they would be happily married to their original spouses today.
While it's true that there are happy marriages that start as affairs, they are in the minority. Only about 5% of all affairs end in marriage, and only about 1/3 of those marriages survive the first five years. You probably have one chance in 100 of turning this marriage into a successful relationship, and you're off to a terrible start in spite of your love and commitment.
I have a theory about why marriage after an affair is so unsuccessful, but the fact that they're unsuccessful is well documented. My main contention is that for whatever reasons, those who have affairs tend not to follow one of my cardinal principles for marriage: The Policy of Joint Agreement (never do anything without an enthusiastic agreement between you and your spouse). They tend to do what they please without considering each other's feelings. While that may not apply to both members of the relationship, it almost always applies to at least one of them. Your friend's affair with another man in the beginning your your relationship is evidence that she's not thinking about your interests.
I try very hard to keep these marriages together, in spite of the fact that there is such a low probability of success. If I thought I would fail, I wouldn't be wasting my time. And yet, I have had very little success. I keep thinking that I will eventually find a way to succeed.
There are so many obsticles to overcome. In addition to failure to follow the POJA, there is also a marked failure to follow the Policy of Radical Honesty. They tend to be incredibly dishonest, in spite of the fact that they start out thinking they can look right into each other's very souls.
Also this
As it turns out, most affairs end within six months of their seeing the light of day (being revealed to their family and friends), and almost all affairs end without leading to marriage. Even those few that end in marriage have only a 25% rate of success.
That's because affairs are based on dishonesty and thoughtlessness for the feelings of others. That same dishonesty and thoughtlessness eventually turns on the lovers themselves, and the affair is destroyed by those same flaws that made it possible in the first place. What drives affairs is passion, not commitment, and once the passion wanes, there is nothing to help the lovers restore their passion.