Hey and welcome to the forum. Sorry you are going through this right now. Im glad you decided to go NC. This is so important for you. You need this time to focus on yourself. I know the urge to call, text, email is there. But you have to fight the urge. Think about it where will it get you. The answer is it will just set you back more. I should know I have made all the mistakes. You have to think with your head not your heart on this. Your friends are right you do not owe her any exlpantions. She broke up with you. There are consequences for her actions. Do your best to stay away from face book and all that other stuff. Good luck with the challenge. You can do it just be strong.
As for the gym. If you really do not feel like seeing her I would just switch gyms if its not that big of a deal.