So, he let you 'listen' to a couple messages from her and that sums her whole attitude and life up for you? You are sitting there, with her husband, listening to her messages. I can't imagine why she might get a little agitated from time to time...
The bottom line is, you only know ONE side of the story and that's the one he CHOOSES to give you. He can claim all the crap he wants to about her, but it's only his word and at this point, he's betraying her, the kids and yes, even you. So, why would you feel so comfortable in just taking his word? Why doesn't he love you enough to make this right? He's supposedly 'trapped' in a horrible marriage with a horrible person...yet, it's not bad enough to leave it for you. Wake up.
Also, you claim you have no responsibility in this. Wrong. You're an adult. You had responsibility from the beginning, to make sure you are getting involved with someone who can be trusted, someone who is available. YOU owed this to everyone involved, including yourself...far MORE than she owes you anything. YOU walked into her life without her inviting you and you expect her to be cordial to you now and give you what you want? Again, wake up.
You are both adults, acting like spoiled children, blaming other kids for your poor behavior. I think it's time to grow up...both of you...and do the right thing.