I think that people who have affairs with committed ones chases the impossible love. They do not have enough self esteem to be wholly loved and they have a unreal fantasy about love so they hang on to a relationship that's doomed to fail. They don't actually want that things end well.
Guess that's why the statistics says that only 10% of A turn into a real relationship.
I think that it may be the case of OW here. She's had 2 affairs. She's seeking but not wanting to commit. Your H will find that out soon.
