One of the major fallouts of an affair is the blow to the betrayed spouse's self-esteem. Your partner or your now ex may have had an affair with someone who to all intents and purposes is nothing more than a plain Jane, which asks the question what does she have what I haven't got? The fact is she has nothing on you. To start with her moral compass was completely non-existent to do what she did but also she cannot truly value her self worth if she is prepared to stoop so low as to have an affair with someone who is already in a relationship. However, I digress. Her issues are hers and hers alone and the man she chose to have an affair with has to deal with those problems now, not you. In the meantime you, as the betrayed, have done nothing wrong and you need to realise that. That starts with building up your self-esteem to the point that you can truly hold your head up high with pride.
...Why does the pain of an affair hurt so much? That question can only be truly answered by those who have experienced it, and as someone who has, I hope this blog can offer some insight to the agony that you are facing.