My wife did exactly the same thing. She told me she wanted a divorce right out of the blue.
She has also showed a nasty side to her which which was not present during our 15 years together. No talk of our relationship, straight to divorce courts.
I do not know if this the same here, but my wife was waiting for an 'excuse' to have an altercation to announce the bomb. All WAW's have a plan, mine did, she told me later that she had 'planned' the moment she was going to tell me.
Listen to Puppy. The script here is similar to mine, and I found out later she was in a PA with a gym 'friend' of mine. I hope this is not the case here, try to gather some information.
Has she been physically distant lately, staying out longer, keeping her mobile with her at all times?
Bomb dropped: 19/12/08 Me:48 WAW:41 D:10 S:6 Married: 15 years