Spells will only further what is already in motion. And thus, if nothing is in motion, then nothing will be furthered by the spell.
You could do a spell to have sexual dreams, or perhaps you could even begin working with incubi/succubi. But unless you are already sexually close with someone, I wouldn't bet on a spell allowing for sexual interactions with another person.
Lastly, if you are tired of masturbating, then simply stop. (Or at least take a break for a while) Alternately you could invest in quality pornography that would better hold your attention.