That is exactly what happened in my situation, W takes an Affair Partner, refuses to end it, moves out, I file legal separation and she counters with Divorce.
My L said this is not uncommon and is a natural reaction to "What you served me with a separation, well then here is a Divorce!" kind of thing. Its very immature in my opinion.
Yes, in my case too, I was trying to hold on with a separation. Obviously it did not work.
I suggest not telling your H anything else about what you are planning to do legal wise. It is showing your hand. This will work against you. Stop talking to your H about your D, let the lawyers talk it out. Anything you say will be used against you. It's tough to hear, but the truth. You were trying to be transparent, and do the right thing. He on the other hand has betrayed you, lied to you and is now divorcing you all while crying he doesn't like hurting you. Really? How is he trying not to hurt you? His actions have proved otherwise.