Stepping Out: If she's not giving you sex, you can go get it from someone else.
Walking Away: If she's treating you like shit, you can leave her and never come back.
These are your two most powerful weapons.
Her weapon of withholding sex is only powerful if you won't get your needs met elsewhere.
Her weapon of disrespecting and bitching is only powerful if you won't ever leave her.
Marriage is the surrender of these supreme male powers, and that's why it's so potentially dangerous, and so rarely successful.
These are your nuclear options, and it's better if you never have to use them, but it's foolish to give them away without very careful consideration.