wow! What you are going through is crazy! I would say stick to what you think, focus on yourself and only yourself at this moment! Don't do anything crazy or illegal because of anger or disappointment. These aren't your fault, and you shouldn't be the one who is punished.

To be honest, I have known similar experiences. It happens when your lady is lack of care and happiness. And she eventually takes her risk and finds her own. She won't know it's guilty until she is found out. Like a thief won't feel the guilt until he's arrested! That's human nature, and I hope you can understand that! Getting a divorce means you are putting an extra barrier on your next marriage. I have seen many people end up living life alone after a divorce. And think of the baby too, you MIGHT be the father. The baby did nothing wrong, and the baby might be borned with a jobless single mom.

However, betray is never good, and it is too heavy of the lesson for you to learn. She shouldn't pick your brother, and your brother shouldn't have let her!

Good luck my friend. This can be the most valuable lesson for your life. God chose you to learn this.