First of all, let's examine possible motives for casting love spells.

1. You are enamoured with someone (you cannot say you love them), and you wish to know them well enough to decide if you can love them.
2. You are lonely and want someone to play with.
3. You have an acquaintance whom you think would make your "perfect match."
4. You know an attractive person and just want to have sex with them.

1, 2, and 3 are decent reasons to cast love spells, even though they will likely not give you the overall results you want, which I'll explain later. D would be better solved with a seduction spell, and I'll tell you why:

Love is something that involves a great deal of a person's attention, time and unfortunately money.  Sex is something that can be dismissed in the morning. Therefore, if you're after someone just to make them a sexual conquest, do NOT attempt a love spell on them.  It's harder to do, it's harder on them, and it's harder to ditch them once you've had your fill of their body.

How do love spells operate?  How does love operate?  Love operates when one person assesses another person favorably (and people assess everyone they meet as potential mates, first and foremost).  A certain attraction ensues, and if both persons are compatible, they fall in love.  Bear in mind that love alone is not enough to maintain a relationship.

Now!

Love spells operate by disrupting this principle of assessment.  When you cast a love spell on someone, it's almost certain that the target of your spell (we shall call "victim") has already assessed you as a potential mate, and declined for any number of reasons.  What the love spell does is cause them to reassess you, while impairing their judgement so they will judge you favorably.  RIGHT THERE is the problem with love spells, and why they almost never bring actual happiness.

When you impair someone's judgement, they become confused.  They also begin to make other mistakes due to this impaired judgement.  Perhaps this poor judgement will extend into financial, employment or hygiene standards.  At any rate, the victim certainly becomes confused, perhaps on many levels.

When the spell causes them to find themselves attracted to you, you become the rock to which the victim clings in this storm of confusion.  What results?  You have a perpetually impaired lover who thinks you are the greatest human being alive, and the solution to all their problems.  You also have a lover who is no longer the same person with whom you originally became enamoured.