For everyone saying get a therapist- they are expensive- mine is $200 an hour! (Though it is true you may be able to find a helpful counselor through your school if you are a college student). Also, most conventional therapists would classify you and put you on drugs- NOT helpful. What you need is a healer, someone to help you learn how to love yourself and understand why you currently don't.
I have never been bulimic but struggled with self-harming issues for years (which therapists often group in with eating disorders) so I understand how hard it is to leave this behavior/need/addiction behind. You say that there are periods where you go without it and eat healthy and treat your body well, and this is a GREAT start!!!! Trust me, that is the first step. Relapsing is inevitable until you come to a point where your love for yourself outweighs the impulse/desire to binge/throw up.
This happened very gradually for me- it started as I learned about nutrition and how my body works, what I need to be healthy, and how food is good and necessary. From there I got into yoga, and meditation and read a host of self-help books the best one being YOU CAN HEAL YOUR LIFE by Louise Hay. GET THAT BOOK! You can get it on Amazon for $10. Also, get the You Can Heal Your Life Companion book and do the exercises in it, they are so incredibly helpful. Most self-help books containing valuable information, but never really drastically altered my life. This book did. It taught me so much and I've come to a point where self-harming simply does not work for me anymore (as you can come to this point where binging/throwing up just will not produce its usual effects). Sometimes I still struggle when I am feeling very low, but I now have ways to curb the desire and I also just know that it will make me feel worse if I do it- so I don't and instead I try to treat myself as I would a little child- with love and compassion.
Trust me, you can heal and you have the capacity to overcome this. I never thought I would get better- but I am SUCH a different person today than I was years ago.