No one can know. Lots of people, especially on mn, insist there's a woman in the back ground when there isn't.
My mum insists my dad left for someone else. He met his girlfriend 6 months after they split.
My exh insists I left the marriage for my now dp. I didn't. I hadn't even met him until we split up.
No survey on this is ever going to be accurate. Because people won't alway answer honestly.
In my opinion, from people I know, both sexes do this. I know my nest friend is incredibly unhappy in her marriage. I have noticed changes in her behaviour, towards other men. I am predicting that she will wont leave, until she has feelings for someone else. At the moment she is just plodding along. He has been a massive shit in the past. But seems to have woken up in the last year or so and is behaving. But i think its too little too late. My opinion is that if he met someone, he wouldn't leave. He would try and have both.
But looking at my wider circle, both men and women have done this. Both men and women have walked away, with no one.
I do think that, generally, women tend to leave it longer before starting to date. Or at least keep a new relationship quiet for a longer period. Men I know who have left with no one else to go to, generally out their relationships very early or at least make no attem6to be discreet about it.