Siddhartha, by Herman Hesse, is a novel which follows Siddhartha's quest for self-discovery. While physical intimacy should certainly happen within a true, loving relationship, love is obviously not a requirement for physical intimacy. Siddhartha meets Kamala after he gives up his quest for religious (spiritual) knowledge and determines to dedicate himself to physical pleasures (not love), instead. Kamala is a courtesan who is schooled in the arts of physical love; because of her profession, she is quite adept at pursuing physical intimacy without the necessity of love. 

Aside from their physical relationship, the two of them are drawn to one another by a kinship of their souls. Siddhartha says: 

"You are like me; you are different from other people. You are Kamala and no one else, and within you there is a stillness and sanctuary to which you can retreat any time and be yourself, just as I can. Few people have that capacity and yet everyone could have it."

While their relationship is not based on love in the traditional sense, they do have a kinship and connection. Later in the relationship, Kamala accuses Siddhartha of being unable to love anyone, and he agrees with her. He says,

"I am like you. You cannot love either, otherwise how could you practice love as an art? Perhaps people like us cannot love."

And perhaps that is the truth of it. The relationship they have, though dependent on physical intimacy, is the only kind of non-spiritual love they are capable of; finally Siddhartha grows bored and leaves. Kamala loves Siddhartha enough to have his son but raises him in the same materialistic lifestyle which was part of what kept her from loving beyond the physical.