You should perhaps consider the fact that when chasing other women for the first time, we tend to put in a lot more effort than in a relationship that has been ongoing for 20 years. You should think about why she lost the spark for you and whether its something you've stopped doing or efforts you've stopped showing towards her after being together for so long.
There's always a chance to win her back, especially when it comes to matters of the heart. Spend this time focusing on yourself and improving aspects of your life that can be worked on, essentially, become an improved version of yourself. Regaining her trust is definitely no easy task, but as long as you are consistent in your effort and the relationship she shared with you was a meaningful one, there's always a possibility where she comes around.
Chances are that you are here because you are still very much in love with your ex boyfriend. If this is the case you will likely be wondering how to make him want you back. When you listen to your friend at this time they will be telling you to get over him and move on with your life. This is a lot easier said than done and not the advice that you want to hear right now. If you really do believe that he is the right person for you, then you will have to do some work and not be dissuaded by well meaning friends. If you are determined that this is what you want to do, you will have to have a good plan. With the help of the experts, you will learn how to make him want you back again and even make his love for you stronger than it was before. You have to be proactive though, so let's get started. /injects>