Sex =/= love.
No one owes anybody else sex.
No one ever 'fails' to offer sexual companionship.

If it's really that important to one person, then the two partners should sit down and discus it, perhaps consider seeing a sex therapist. Work through it. That's all anyone is 'allowed' to do.
But if "No sex. Wah." is the sole reason for relationship issues, than that's a pretty low reason to go behind someone's back or anything of that nature, if you ask me.