The analogy between interpersonal relationships and chemical processes is well-established. Just about everyone understands what it means when you say, “we just didn’t have chemistry”. In fact, according to the Online Etymology Dictionary, this usage goes as far back as the 18th century. The analogy can be fleshed out by the light-hearted addition of such concepts as “single displacement reaction” and “activation barrier”. Now, anyone who hasn’t taken a chemistry course is going to give you a funny look because they won’t know what you’re talking about, but I suppose that’s the price you pay for unlocking the “Used Chemistry Terms in Casual Conversation” achievement. (Wait, what do you mean, you don’t keep track?!)
I think I’m a bit odd, though, in actually taking the analogy seriously. A lot of people seem to have a fair amount of faith when it comes to their love lives: they don’t know how or when they’re going to meet their lifelong partners, but they’re sure it’s going to happen. What I believe, though, is a bit different: the system will eventually reach equilibrium, if you allow it to. I don’t postulate that you’re guaranteed to meet that special person, but I do submit that if you meet them and keep in touch for long enough, then you’ll eventually end up together. Furthermore, if you’re with the wrong person, it won’t last long.
Indeed, I like to imagine a spring between every pair of people. This spring doesn’t exist in real space, but an abstract space in which the distance between two people measures intimacy (greater intimacy means shorter distance). I like to say that every spring has an equilibrium length, which corresponds to how compatible you are, and that eventually, all those springs are going to reach equilibrium. If you’re not very close to someone whom you could be closer to, you’ll feel the desire to get to know them better—that’s how strangers become acquaintances, acquaintances become friends, and friends become… well… more than friends. That’s the restoring force. (Did I just wade into physics territory? It’s worth noting that the model of chemical bonding with a harmonic potential between two atoms is commonly taught in physical chemistry courses.) If you’re too close to someone, it’s going to come to an end eventually—the restoring force pushes you apart. Equilibrium is not always reached right away—for example, you might be dating, then break up and not talk to each other for a few months, but then, after a long period of time, you may be friends again—and that’s where the equilibrium distance might lie.
I also like to imagine a diverse set of protein molecules floating around in a solution. Some pairs will have very high binding constants; once they bind, they’ll stay together, for the most part… perhaps by chance a high-energy molecule will come by and break them apart, but they’ll be together again, sooner or later. A binding that isn’t very strong won’t stay together for long—it may break apart of its own accord, or a single displacement might occur. It’s important to note, of course, that two molecules are not going to end up bound together if they never come into contact. (Just like in real life.)
In a sense, then, what I’m saying is: if it’s meant to be, it’ll happen. Sooner or later. This is the attitude I’ve consistently taken whenever I’ve been plagued by anxiety-inducing hypotheticals. If you mess up, but the other person likes and understands you well enough, it’s recoverable; you’re only separated temporarily while the equilibrium re-establishes itself. (This is true of not only intimate relationships but also friendships.) If you feel like you “missed your chance” to make your move—well, it’s never too late—the most stable configuration awaits you. And if the person you love actually ends up with someone else—that person probably had a higher binding constant with them than you did… but not to worry, someone better for you might still be out there.
The only thing to watch out for here is that you don’t ignore the non-equilibrium regime. (Apparently, non-equilibrium thermodynamics has not been extensively studied, which is why equilibrium thermodynamics is very well understood, and non-equilibrium, not so much. This makes it difficult to study, among other things, biological systems, which are only interesting as long as they stay away from equilibrium… that is, alive.) So if the right person comes along, you don’t have to worry about how things will work out—they will. But it’s still worthwhile to consider what happens before that. A lot of people out there are in non-equilibrium relationships—sure, they might not end up married to their current partners, but many of them are still having a good time. You may as well seize the opportunity to enjoy non-equilibrium interactions if possible—after all, there’s no guarantee that you’ll meet that special somebody within your lifetime.
The disconnect between equilibrium and non-equilibrium thermodynamics is a source of some of what you might consider bad advice going around. For example, “be yourself” is good advice in the equilibrium regime—indeed, it might help equilibrium be established more quickly—but not so much in the non-equilibrium regime: if you just “be yourself”, but that isn’t a person that most people can relate to, you may end up with no non-equilibrium interactions. Nope—if you want to form that short-lived unstable species, you’ve got to pour energy into the system. Unfortunately, in this I have no advice to give. If I figure anything out, I’ll let you know. ;-P
B³₂ 
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