I regret not having links to share, but studies show that married people on average have sex more often than unmarried people. Protestant couples (married) report having the most sex of any of the cohorts studied, though catholic couples had the highest subjective satisfaction rating - make of that what you will.

My interpretation: this is largely because most people, when they are single, struggle to find romantic partners. Many are also (at least ostensibly) looking for someone to marry, and so they try to optimize for that (sometimes) at the expense of more sex now.

I agree with the distinction you are making though.