Bulimia and my best friend? I need help?

I suffered from bulimia for about six months last year, and managed to stop the throwing up, mainly via the help of my best friend. However, I recently threw up again for the first time in those six months, and so naturally I went to him for help. He later td me that he blamed my bulimia relapse on himself because he "couldn't help me enough". No matter how much I told him that it wasn't at all his fault, he still believed it, and I ended up promising him that I wasn't going to throw up anymore (big mistake). However, there have been a few times where the disorder took over and I felt like I NEEDED to... I didn't tell him because I thought that he would blame it on himself again, and of course I feel terrible for breaking a promise. And making one I couldnt keep. So my main question is, should I tell him that I broke the promise? I hate keeping things from him, because I never do, but at the same time.. I feel so guilty :/