It is unfortunate that you found out how your wife is feeling in such a shocking and painful manner, but at least now you know. It sounds like your marriage is in serious trouble. Chances are that she was just venting to a friend and, thinking that it was confidential, was overly dramatic. I doubt that she really wants you to die, but it is clear that she is hurting and desperate.
If you really are being abusive in any way toward her, I hope that this email serves as a wakeup call and you will seek help immediately. Posttraumatic Stress Disorder is a serious condition, but it is not an excuse to abuse another person. There are many successful treatments available.
On the other hand, if your wife is mentally unstable and you believe that she really did mean what she said, then you would both be better off getting divorced and going your separate ways. Love is not enough. However, if you want to attempt work through this, I would highly recommend that you only do so with the help of a marital therapist.
All the best,
Dr. Holly Counts