Celibacy during magical initiation is a must. All initiates of the ancient schools of magic needed to be celibate until mastery. Today I would like to discuss the reason behind that because it is as relevant now as it was a thousand years ago.
During initiation, which usually lasts a year or longer, the aspiration is to develop the magic to the highest degree, meaning you will need all of your most potent fluids.
In promiscuity, it is not so much that you are being "immoral" but it is more that you are removing from yourself, deducting from your destiny. Sure, if every person you sleep with is of magical lineage, then that would be good, but with the percentage of people on Earth who have that, your chances are close to nothing! Promiscuity is a quick way to water down your own attributes; it is like you're burning your own self at the stake!
Who is the magician?
"They are without fears and without desires, dominated by no falsehood, sharing no error, loving without illusion, suffering without impatience, reposing in the quietude of eternal thought... a Magus cannot be ignorant, for magic implies superiority, mastership, majority, and majority signifies emancipation by knowledge. The Magus welcomes pleasure, accepts wealth, deserves honour, but is never the slave of one of them; he knows how to be poor, to abstain, and to suffer; he endures oblivion willingly because he is lord of his own happiness, and expects or fears nothing from the caprice of fortune. He can love without being beloved; he can create imperishable treasures, and exalt himself above the level of honours or the prizes of the lottery. He possesses that which he seeks, namely, profound peace. He regrets nothing which must end, but remembers with satisfaction that he has met with good in all. His hope is a certitude, for he knows that good is eternal and evil transitory. He enjoys solitude, but does not fly the society of man; he is a child with children, joyous with the young, staid with the old, patient with the foolish, happy with the wise. He smiles with all who smile, and mourns with all who weep; applauding strength, he is yet indulgent to weakness; offending no one, he has himself no need to pardon, for he never thinks himself offended; he pities those who misconceive him, and seeks an opportunity to serve them; by the force of kindness only does he avenge himself on the ungrateful..."-The Threshold of Magical Science