You know that feeling you get when you first fall in love? Weak at the knees, stomach churning, can't think about anything else? It's great, isn't it? On the other hand, it puts you on an emotional roller coaster that makes almost everything else, from work to eating, really quite difficult.
Some people get addicted to it. They just don't feel alive unless they're "in love." Of course, relationships don't stay like that. Sooner or later you become confident and sure enough of your partner not to worry and fret, and you get used to having them around so you don't jump at the sound of the phone. So if you're addicted to falling "in love," you'll have to keep ditching your partners and finding new people to fall for.
You may be wondering why I keep putting quotation marks around "in love." Well, there are two reasons. The first is that you don't have to be in love to have this feeling, and you may be misled. It might actually be lust or infatuation and not love at all. The other reason is that I don't want to imply that if you don't have this feeling, you aren't in love with your partner.
There are very good reasons why this heightened emotional state doesn't last forever. You couldn't function, and the state has a lot to do with nerves and excitement, and after a while your relationship will inevitably stop making you nervous and cease to be as exciting as it was. You can still do exciting things together, but the relationship itself will become routine, hopefully in the very best of ways.
So what do you end up with if you stick out the relationship past the point where you can't sleep at night and can't think about anything else? Well, that varies. For some people what's left isn't really worth having. For those people who have a combination of luck, good judgment, and a grasp of the Rules, what you can end up with if all goes really well is contentment.
Contentment isn't about fireworks and weak knees and butterflies. This is why some people completely fail to realize that despite its more subtle charm, contentment is worth a whole lot more than short-term passion. Being content with someone doesn't mean you're no longer "in love." It means you are truly and deeply in love in the best sense without any quotation marks.
So don't get hooked on getting that fix of first "love." Concentrate on making sure that you follow the Rules so that as the first flush slowly dies down, it is replaced by something that is more rewarding, companionable, warm, fulfilling, and loving. When that happens don't think about what you have lost but about what you've gained. That's contentment -- and you should be more than happy with it.