There are many reasons why an affair happens. Rarely can an affair be narrowed down to a single root cause. Sometimes factors in the relationship have the greatest impact, other times problems with the individual contribute most to the affair.
Let me first explain internal vs. external sense of self worth. People who have an internal sense of self worth know they are valuable simply because they exist. They are aware of their own strengths and have a positive view of themselves regardless of their current circumstances. It’s not that they don’t see flaws in themselves, but they understand flaws are normal and they don’t need others to validate them to know that they are okay.
A person with an external sense of self worth relies on people outside of themselves to validate their worth. Someone else must recognize their strength and worth for them to think they have any. For example, a boss must verbalize appreciation for their work or they feel useless. If no one recognizes them, they must not have value. This person is vulnerable to having an affair.