The essence of a situationship is perpetual options, a romantic relationship wrapped within a friendship framework.

It sounds good, but there are two problems:
1. Perpetual options with no holding costs are absolutely unfavorable to the seller.
2. For the buyer, not all options are worth holding (such as deep out-of-the-money options, fundamentally poor call options, options with implicit holding costs).
The essence of a romantic relationship is a perpetual option with a funding rate, where both parties have holding costs, and if the costs exceed the potential benefits, they will close the position and walk away.
The essence of marriage is a lock-in contract with huge exit costs, similar to fund LPs, large fixed-term deposits, partnership equity, and commercial real estate.
Interestingly, the preconditions for marriage often include large fixed-term deposits and commercial real estate. Choosing marriage too early is equivalent to locking all your liquidity, and even locking your parents' liquidity, often requiring loans to lock in.
This kind of riskless, no-profit investment is not rational, which is why marriage rates are decreasing.