My situation was a bit different... in NY, a sexual R outside of marriage *is* considered cruel and inhumane. But yes, you are correct, to file under adultery you need to have tangible proof or a 3rd party witness say they observed the spouse and OP having sex.
I asked my H for a separation, he said no and hired a snake of an attny. Our litigation went on for 18 months. Once my H figured out I was not going to back down or roll over and I would not accept the BS settlement things changed. I countered his suit w/cruel and inhumane treatment and in my supporting statement (which you have to include when you file or counter) I spelled out EXACTY what was cruel and inhumane.
The judge set the trial date and the night before the trial, it was requested by my H and his counsel we legally separated. I said no, sorry, too little too late. They knew what would come out and then my H had *little* chance to get even a fraction of what he thought he would get.
I agreed to the separation THREE hours before the trial if my H granted me 80% of our liquid assets, had to pay me the cash value of our vehicle at the time of purchase, pay off all the debt (which was his from OW anyhow), pay my health insurance and spousal maintenance, remain the sole beneficiary of all his insurance/retirement/investment accounts, I kept the marriage residence and all our furniture and he had to pay ALL my legal fees. The fool agreed so I took it and ran. I guess he had to decide what was more important... lost money or a trial that spelled out exactly what had been going on for 2.5 years in his bedroom. That wasn't my doing, it was what the judge said when he dicked around with a settlement for nearly two years.
My offer was so ridiculous my attny said if I somehow got my H to agree I was nothing short of a genius. No, I am not a genius I just played my cards in the best way I knew how. He had the option to separate "easily" in 2008 and to please his GF he said no. Funny how 18 months later he couldn't separate fast enough.
He narrowed his options, not me. I just used his lack of good judgement in my favor.
