It’s normal for the sexual part of a relationship to cool off a bit, but what you’re experiencing seems to be more than the normal decline. And my guess is that the cause isn’t sexual but something else. I know you say the relationship is perfect, but I have my doubts. It doesn’t have to be something huge, but I say there is something nagging at the back of your mind that is causing you this problem. So look beyond the sexual arena and see if you can discover what else might be making you feel this way. If you can discover the real cause, you’ll have an easier time figuring out what to do about it.