i don't think you need 'evidence' to divorce
You don't need evidence, but the wife can simply say "Lol, no," and that's it, no divorce unless you take other legal routes that’ll drain both your money and mental health hard.
Gathering evidence makes things easier, and push things in your favor because, as you said, you can even sue the parties involved.
Oh, you can also do what a few dudes I know did: just leave one day, wait 3–5 years, visit family court, get a free consultation, prove you haven't been living together all that time, and Ta-da!
Divorce acquired, even without the partner's consent.
(The process isn't exactly this easy, but it's an option)