The institutional framework is not intended to resolve emotional problems. When you rent an apartment, there is no guarantee that you will feel emotional comfort often associated with the word "home." Indeed, nobody in his right mind would expect such a guarantee. That, however, does not prevent the parties from signing a lease agreement that outlines very specific responsibilities of each party, i.e. when the rent is due, which repairs are the responsibilities of the landlord and which of the tenant, termination of the lease, amount in escrow to cover potential damage, etc. etc.
Ditto for personal relations that involve property and social responsibility. You can define marriage or intimacy whatever you want, but that is very different from signing a legally binding detailed agreement about responsibilities and rights of each party which should be a condition of a legally recognized 'civil union.' That would solve many problems, including children getting married to fulfill their wildly naïve dreams, homosexual marriages, dysfunctional marriages, etc. The bottom line is that emotions and subjective meanings are clearly separated from the legally binding contract - just like in you lease agreement. Anyone with pre-defined legal capacity can enter such agreement and enjoy equal protection under the law in enforcing the terms of that agreement - but any emotional, spiritual, religious, cultural or what-not meaning attached to it is just a private matter of the individuals involved.
So to answer your question - if the contract provides that a party must be sexually satisfied by the other party, then yes, the lack of sexual satisfaction can be the grounds for terminating the contract. But if such provision is lacking, then the contract is valid regardless of what the sexually frustrated part may feel.
I guess having to sign a detailed contract instead of making vague vows would put a wet blanket on many hastily entered marriages. What is more, separation of subjective emotions from legally binding contract would solve the problem of "gay marriages" - anyone can enter a legally enforceable civil union contract, but the state stays out of the subjective/emotional/spiritual/religious meanings that individual parties want to add to that contract. Just like the courts can enforce your lease agreement, but cannot define whether the leased property is a "home."
Wojtek