How do you think God looks at, e.g., open marriages where one or both spouses can engage in sexual relations with whomever they want outside of the marriage?  After all, we are taught to "love one another," and what shows love more than sex?

I don't think God wants us to rationalize away our sin; indeed, that temptation to rationalize is precisely what He wants us to resist.  We have to choose God over self.