Simon says, “Give the relationship your best shot.”
You know Simon well enough by now to know he would not recommend anything less. Doing the right things right, the first time, on time, every time may indeed be his theme song. It likely comes as no surprise he is now singing that old song in reference to long-term relationships. “Relate the best you know how, every chance you get.”
A long-term relationship is not a now-and-then, if you feel like it or have time proposition. Neither is it a place where less than your best will do, unless you do not care about risking the relationship. Sure, that level of effort and commitment benefits your significant other. You do it for them; and that is certainly thoughtful of you. More to the point, though, giving it your best shot every time is in your very personal self-interest. Do it for you.