Could you explain when using bulimia to lose weight, does brushing your teeth stop them from rotting?

See your PCP. Brushing your teeth after you vomit can contribute to tooth decay. Treatment for bulimia involves psychological counseling, nutritional counseling and medication such as antidepressants. See your PCP for consultation. Do not delay.
Dangerous practice. There are much better ways to loose weight. Please talk to someone about your bulemia. This is a dangerous thing to do. As for your teeth, it is the acids that will erode your teeth. The worse thing to do is to brush your teeth immediately after you purge. This is when the teeth are at the softest. Use baking soda to counteract the acids. Get help with this.