The institutions of men have no power over God. The body of Christ is not a manmade instution. Marriage is not a manmade institution. To say that any of our created systems supersede divine truth is to debase what is sacred.
Salvation is not limited to the manmade church, because it does not supersede the heavenly Church - the body of Christ - the foundation of which is God-given revelation of Christ. How can you believe that salvation is only through a created institution that has been subverted?