eating disorder.

When I was 15-16 I suffered badly from an eating disorder. I'm 18 now and I've had a period of time that I've been no longer focusing on my weight (only because I'm happy with the size I am...) I went from 65kg to 50kg, I'm 5'6 (I currently weigh 55kg). I'm now in a relationship and those feelings and habits are slowly coming back... I'm unsure of how to and if I should explain to my partner my history and how it works ( as in how it effects me...) he doesn't understand these sort of things & doesn't understand why I'd suffer from it.