There’s a lot of stuff that changes about a person after living with a person they’re dating, after a while. There’s the Big Stuff, of course—ideas about the future, the possibility of personal identity in coupledom, masculinity and femininity, all that stuff.

Then there are the Specific Things, particular to each person. The messy learn to become neater, the antisocial get used to being dragged to parties, the disinterested-in-television start to enjoy watching Top Chef or Rock of Love or Gossip Girl -- the gradual blending of personalities that takes place when two different people make the thousand compromises necessary to successfully cohabitate.

As a side note, I think it is the general unwillingness of a person to make these compromises outside of a romantic partnership-type cohabitation that makes some people terrible roommates. (Like me! Sorry, former roommates!)

But lately I’ve been thinking about the third and much more elusive type of change a person undergoes when living with a partner: changes of a more obscure origin. These are instances where one or both persons in the couple suddenly change a way of thinking or living for no real reason that makes sense. I’m sure you’ve observed this, either from the inside or out.

For example, the pair that always loved sleeping in on the weekend that suddenly are all out and about by 9 am. Sudden conversions to vegetarianism by a person previously uninterested in the idea. A former hater of live shows suddenly going out to see as many people as possible. Now to be fair, any of these changes could be related to aging, coincident to cohabitation, or prompted by a million factors unrelated to living situation. I understand that.

I just know that for me, certain behaviors I have have changed in a way that I know is somehow related to living with Frank without actually having anything to do with Frank. Example: sharing food. I have always hated sharing food. Despite growing up in a household that was always filled with delicious, well-prepared meals and abundant, freely-available snacks, I always had an irrational fear that if I agreed to split dinner with someone, that I would not get my fair share and therefore go hungry.

Even if it was at a tapas place where I knew intellectually that I could order more if I needed to, or in the situation where you order two full-sized entrees and each eat half of the other’s—therefore still getting an entire entrée’s worth of food—I still had a sort of irrational panic that I would come away hungry. (Which in and of itself is weird, I mean, if I left the dinner table hungry, I could just get a snack, right?)

It was worry that I ate more than the average person combined with the notion of radical fairness above all that I had at the time. I realized the other day as I was out to dinner with some friend that I was trying to talk into splitting a couple appetizers with me that I had, at some point in the recent past, abandoned this weird habit.