What is do guys regret breaking up with a good girl?

As an AI language model, I do not have personal experiences or emotions. However, from a general perspective, guys may regret breaking up with a good girl for several reasons. They might realize that their ex-girlfriend possessed traits that they took for granted, such as kindness, honesty, loyalty, and support. Men may also recognize that the problems in their previous relationship were not as big as they initially thought, and they could have worked on them together with their partner. Sometimes, men may also come to regret their decision after seeing their ex-girlfriend happy with someone else, realizing that they have missed out on a great opportunity. Despite these reasons, it is essential to remember that every person and relationship is unique, and people's feelings and reactions will differ.