MADE A FOOL OF MYSELF

So I broke down and started seeing NARC about 2 weeks ago. Reconciliation only lasted about a week. In that time I saw on my meetup.com site that he sent messages to a particular female with a motorcycle and he asked her when she could get out and ride. Naturally, because of past infidelity (x's 10)...I have a hard time trusting him. So I emailed said woman and asked her of he had tried to talk to her at the same time he was begging me to come back... she sent a nasty reply back.. pointing out that I do not trust him and never to contact her again. She CC'd his email with the whole conversation after I asked her to keep this between us. So now I'm mad because I feel like he was not being honest but I was wrong in my assumption as to who he was talking to. She seemed mad at me when I just genuinely wanted to get the truth... So was I wrong to email her? Was she right to be angry with me?

In any case I'll take it as a lesson learned. She has no idea what I have dealt with so I guess I can't expect her to understand.