What should someone who suffers from OCD and bulimia do when they swear to stop eating but then break their oath, and how can they atone for that?

It is recommended to treat obsessive-compulsive disorder with ruqyah (Islamic exorcism), medical treatments, and reliance on Allah, not by swearing oaths. If the oath was made without intention or will, then nothing is incumbent upon the swearer, as an oath is more deserving of an excuse than a divorce. However, if the oath and the abstinence from eating were done with intention and will, then the oaths become binding and expiation is due for each oath. This expiation consists of feeding ten poor persons, or clothing them, or emancipating a slave. If one is unable to do so, then he must fast for three days. It is also advised to refrain from excessive swearing and not to succumb to the whispers of Satan, but rather to turn away from them.