Fear

Love.
Or moreover, A Crush.
Infatuation. Obsession. Undeniable attraction.
These things amalgamate to create the most annoying yet amazing sensations that are known to human race.
They drive people from sane to insane. At the same time, these kind of experiences give us a lot of chances in life to drive ourselves back on the path of sanity.
The problem, mainly, in these situations, is to keep your mind focused on anything without relating it to the object that has occupied your mind.
You seem to feel insecure and possessive about the things you love. You suddenly become the protector, as if you own it.
The person or object seems to revolve in your mind. You associate a lot of things with your love.
It's insanity that is simply irrevocable.
That's a part of life, we all face it, and always will.