Thinking through relationships in general, I said that belief is the root of all deep and successful relationships.
Now take it to the level of lovers. The root of that is, of course, desire.
I've known couples who had deep respect for each other in personal and professional ways. Their confidence in the other was stellar. But there wasn't an underlying craving in their relationship. Or worse, there was for one, but not the other.
I've known marriages where they couldn't keep their hands off each other, but by one or the other there was a lack of belief in the other. That glue of desire kept things together. Barely, sometimes, but since that kiss and physical romance were so powerful, it was enough.
Why? I think that passionate desire makes it seem like belief. There's no doubt expressed when you're tearing clothes off each other or in the midst of making love. Both partners walk away from it feeling like the object of all the world's affection, ten feet tall, and ready for anything.
Sex can also steal us away from the world, from the problems and worries and fears that can erode our confidence, and give us respite from removed belief.
Physical attraction and mutual respect - the bedrock of marriage and lifelong commitment. Without expressed belief in each other and without mutual craving, things will fall apart.
The question, I think, is how people communicate belief and, in the case of romance, desire to the other person in a way that is heard and convincing. And that starts by listening...