HAPPY VALENTINE’S DAY — NOW, CUT YOUR LOSSES!

If you are 24 years old or have been dating for less than a year, then it’s a little too early to be seriously worried about where this relationship is going. And if you don’t want to get married, then hey, don’t! Breathe a sigh of relief that he didn’t propose, grab a snack and settle down for the latest issue of “The Americans.”

Those aren’t the folks I’m talking to. I’m talking to you, 30-something woman who has been dating the same guy for a couple of years (or more), maybe already moved in together and started picking out that furniture. The one who is ready for those babies, or at least a joint tax return, and would like to get the matter settled as soon as possible. The one who is anxious that her partner doesn’t seem as eager as she is but is afraid to deliver an ultimatum for fear the answer will be “OK, bye.”

Here’s the thing, though: The guy who leaves you because you deliver an ultimatum is probably also the guy who is going to leave you a couple of years later, having wasted more of your prime dating years on his dithering. Pardon the sexism, but most men aren’t operating on the same timetable for having kids, and also, at least in my experience, they don’t tend to stay silent and hopeful for so long. . . .

A sunk cost is, well, like a sunken ship: It’s gone, and you cannot retrieve it, or you can only retrieve it at immense expense. The correct and rational way to deal with a sunk cost is to ignore it — to make decisions without thinking about the money or time you’ve already invested.

It’s very hard to get people to accept that.