While these are often separate themes, the characters in On the Road fail to distinguish between love and sex, sex and marriage, lust and love. Dean marries or wants to marry every girl he lusts after, while Sal only wants sex if there is a loving and soulful element to it. On the Road portrays a sex-without-strings attitude. There is also a holiness, or a spiritual element to sex. Lastly, the character of Dean lusts after very young girls, perhaps suggesting that women are being used as a substitute or representation of abstract desires (youth, for example).
Because he wants a soul connection rather than sex, what Sal is actually looking for in a woman is a female version of Dean.
While Dean cannot satisfy his sexual lust, Sal cannot find a woman to placate his feelings of solitude. These different examples of Beat Generation dissatisfaction reflect the core differences between Sal and Dean.