Analyze Titania's infatuation for Bottom in A Midsummer Night's Dream.
Well, we know it only happens because Oberon has anointed her eyes with the "love-in-idleness" flower. And, Shakespeare makes perfectly clear, it's absolutely an on-sight reaction based on Bottom's (probably awful) singing as well as his physical appearance:
I pray thee, gentle mortal, sing again.
Mine ear is much enamored of thy note
So is mine eye enthralled to thy shape,
And thy fair virtue's force perforce doth move me,
On the first view to say, to swear, I love thee.
Bottom, half-translated into a donkey, is treated like a king by Titania, who demands that her fairies look after him:
The honey-bags steal from the humble-bees,
And for night-tapers crop their waxen thighs,
And light them at the fiery glow-worm's eyes,
To have my love to bed and to arise...
The last line also points to the other obvious thing to say about the relationship: it's probably a sexual one, with Bottom asking for "new nuts", in their awakening scene.
The real question, I suppose, is why Oberon might want to cuckold himself (that is, have his wife cheat on him) with a donkey-man in order to revenge himself on Titania - of course, he does regret it by the end of the play. But the facts are simple: Oberon causes the infatuation, and then removes it with another flower.