It is the maturation of friendship, which makes sex so much sweeter. You must be friends before you can be lovers. Infatuation lacks confidence. When they're away, you wonder if they're cheating. Sometimes, you check.
Love means trust.
You are calm, secure and unthreatened. They feel your trust, and it makes them even more trustworthy. Infatuation might lead you to do things you will regret, but love never steers you in the wrong direction. Love is an upper. It makes you feel whole.