Lama Ole’s answer:
Observe people closely and you will often see what sort of relationship you could have with them. You can see whether attachment arises and what kind of connection it could be—more sexual, more emotional, and so on.
There are four roles a woman can take on for the man and vice-versa. A woman can be like a mother who tries to parent him. Or if the man and woman simply have a lot of fun together, she’s more like a sister. If she is protected by him, she is like a daughter. And if there is physical attraction, she is rather like a lover.
The woman can perceive the man in the same way. He is like a father if he is a protector, giving security. If being together with him is fun but doesn’t involve too many emotions, then he is like a brother. If he is someone who needs to be protected and nurtured, he is like a son. And if he is physically attractive and the relationship flows well, he is like a lover.
Everybody wants to be the lover, of course. This is more exciting and special. But I can tell you, in my experience—and through the blessing of all Buddhas—ten years later, it no longer matters whether someone was like a sister, a daughter, or a lover to me. No matter how close it was, in long-lasting relationships this is not important at all.
Of course one gives more and is more open towards a person one makes love to, since this is a close relationship. But the lasting qualities are much more important, the qualities of the dharma and the quality of trust. What is really important is to grow, to develop ourselves, and to work together.
There is great blessing in being together, but if there is too much attachment, then suffering and difficulties arise too. The most important is to share the dharma—the development and the growth.