In 1486, Heinrich Kramer, a Dominican monk and Inquisitor, published the famous witch hunters manual, Malleus Maleficarum. The text enumerates theological arguments for the existence of witchcraft, and devotes pages to the ins and outs of judicial proceeding, but this is all overshadowed by the its lurid, obsessive focus on sexuality.
Consider this "matter of common report":
And what, then, is to be thought of those witches who in this way sometimes collect male organs in great numbers, as many as twenty or thirty members together, and put them in a bird’s nest, or shut them up in a box, where they move themselves like living members, and eat oats and corn, as has been seen by many and is a matter of common report?
It is not totally clear to me why a witch would do this. Perhaps penises make good pets. What is clear, however, is that a) Kramer was very concerned about the magic of sex and love, and b) the magic of sex and love is weird and confusing. Having read more than a few love spells at this point, I have found that this is bourn out in other magical texts.
There are a wide array of spells devoted to acquiring love and sex. This is one of them:
This is the Grimorium Verum version, emphasis mine:
Write on virgin parchment the Character of FRUTIMIERE with the blood of a bat. Then put it on a blessed stone, over which a Mass has been said. After this when you want to use it, place the character under the sill or threshold of a door which she must pass.
When she comes past, she will come in. She will undress and be completely naked, and will dance increasingly until death, if one does not remove the character; with grimaces and contortions which will cause more pity than desire.
Of course, the biggest problem with this spell is that it is magical instructions for sexual assault. But what sets it apart from all the other deeply not okay spells is that it explicitly warns you that what will happen is not sexy, it's just awful.
Incidentally, it is far and away the most popular spell on grimoire.org.
But let's say you have a different problem: you have an unwanted crush, and would go to any length to clear your head.
This spell appears in The Egyptian Secrets of Albertus Magnus, a comprehensive German spellbook from 1725, with more than 800 spells and folk remedies.
Such a person must put a pair of shoes on, and walk therein until his feet perspire, but must walk fast, so that the feet do not smell badly; then take off the right shoe, drink some beer or wine out of this shoe, and he will from that moment lose all affection for her.
To their credit, this sounds like an effective anaphrodisiac. The book also suggests this alternative:
When you are infatuated and bewitched by a woman, so that you may not love any other, then take blood of a buck and grease your head therewith, and you will soon be all right again.
And what if your troubles aren't just about lust, what if you are really, truly in love? This spell appears in the French grimoire Le Petit Albert, published in 1706, and in the Grand Grimoire from 1821
Grand Grimoire version:
Take a gold ring that is studded with a small diamond that has not been worn by anyone. Wrap it in a piece of green fabric and for nine days and nine nights wear it against your skin over your heart. On the ninth day, before the Sun rises, engrave the following word inside the ring: Scheva, with a new scribe or engraver.
Find a way to have three hairs of the person who you want to love you, unite them with three of your own hairs, while saying: “Body, that you could love me, that your desires could be as passionate as mine, by Scheva’s most potent virtue.” Tie the hairs in a love snare knot around the ring. Wrap the ring in a piece of silk, and wear it against your skin over your heart for another six days. On the seventh day, Fast. On an empty stomach, unwrap the ring and give it to the person you desire to love you.
If your ring is accepted then you can be certain to be loved by that person. If the ring is refused, rest assured that the heart of that person belongs to another and in that case, you should seek your fortune elsewhere.
There are two things that I like about this spell. First, the spell essentially boils down to "if you want to marry her, try proposing." Second, if she doesn't want to marry you, you have to accept it and move on.
It's certainly better than tricking your would-be lover into eating your dung.
 The sigil of Frutimiere from Grimorium Verum: