Actually, you are the one messing with the definition of sanctity. Some people believe that the sanctity of marriage is co-equal with the sanctity of life, and don't feel that "sanctity" is something that can be downgraded and compared.
And in fact, if you look at how Christians practiced in the first few centuries after Christ's life, death, and resurrection, you'll find that they gave their LIVES before giving up their MARRIAGES. You can put your modern twists on things all you want, but remember that not everyone believes that modern society has a better handle on things than back then.
Have a mistress, kill you wife -- but never ever divorce her.
You've caught a moral sickness.