Premarital and extramarital s*x by males and females is a commonplace. Nevertheless it's a ground not only for Divorce but also for avoiding Maintenance. I appreciate this law.
Committed by women, it's never been an offence and, of late, is not an offence when committed by men too. I appreciate this law also.
You must prove such s*x. Otherwise you can't avoid Maintenance.
Even if you can't prove, no Court can compel you to live with her.
By all means abandon her and don't remarry. Second wife will, by all probability, be worse than the first one.