Years ago I was at a house party and found my sister's bf cheating on her with another girl. I didn't tell her, I told him that I knew, and that he had to come clean with her or I would. Faced with the decision, he owned up and told her.
And she got mad at me. I was the destroyer of their relationship because I rocked her boat. Understandable. It was a gut reaction when faced with the loss of someone she loved - easier to target me, the messenger so to speak. Needless to say that we are still best friends and that boyfriend is long history. Time will tell, maybe ex-mil, once she has a chance to process her feelings, will eventually come to see things differently. She may not. But don't take it personally - her world has been shattered and she's trying to cope. You have nothing to be ashamed of. Let the fault lie squarely with the one to whom it belongs.