Young love, new love, new relationship energy, butterflies... does it go away? Sure.
It matures into something deeper, more meaningful, more lasting. That doesn't mean that you never get that jolt of "How did I ever get so lucky!?!" but you don't notice it all the time. It is like being in a warm tub. You acclimate after a while, so that you sometimes don't notice how good you have it, and may even get a little bored or tired of the position you are in, or whatever. But, if you just shift a little, the water swirls, and you notice again how nice it is.
This is only the case if you thought it was great when you got into it. If you climbed in for the wrong reasons, if you never had that great feeling about it in the first place, then it isn't a surprise if you don't find it once you are in. That isn't to say that someone who doesn't feel this way can't have a perfectly acceptable career that provides all that they might want from it... unless what they want is to love their work.
If you have found something that gives you that feeling, and you want to chase it, you should do that. It may not be easy to catch, but if you are always following your passion, you have a better chance of keeping up with it than if you don't even try.
