Assuming she is actually cheating, leave her and get a 20yo gf; nothing breaks a woman more than to see an ex with a hotter chick than her. To fix the heartbreak just fuck other chicks until it goes away.
Otherwise shitty situation, if you can't satisfy your woman in the bedroom she will behave this way. If you want to keep her with your broken leg or whatever buy her a really expensive sex toy that vibrates at mach 10.