I've had crushes in the past, not any real meaningful love, and I would say the longest crush that I've ever had lasted around 3 years. Afterwards, the feelings started to fade. How long your feelings last and how fast they fade depends on the circumstances. I was in the same class as my crush for 2 years in high school, and I get to see him almost everyday, so that didn't help. The more I see someone, the less I forget about that person. After high school, I still had a lingering crush on this person, but we went to different colleges. After a year or so, the crush started to fade.
Not seeing each other face to face everyday does make the infatuation go away. Also, deleting the person as a friend on facebook, deleting the phone number, and not visiting any social media content belonging to the person helps too.