There’s a lot of good stuff here, but who says that every relationship has to progress to long term or permanent? Obviously, if that’s what one (or both) of the partners really wants, then that’s fine, but the “relationship escalator” is itself a source of a lot of issues. Not everyone that we enjoy being with needs to turn into marriage material or even steady monogamous relationship material.
Also, I’m skeptical of the guy who says that lust declines 8% for every year of marriage. I’ve been with my partner for 30 years, 25 of those married. We are still incredibly hot for each other and although we go through some fallow periods, we also still go through periods where we are sneaking into the pantry or the bathroom so that we can be alone with the door shut in the middle of the day.