Is what happened considered a vow that must be fulfilled, and is expiation for breaking an oath (kaffarat yamin) required if it is not fulfilled, and is the expiation repeated with the repetition of the sin, knowing that I suffer from obsessive-compulsive disorder?

Scholars have differed regarding the vow to abandon a sin. Some view it as not being binding because it is a foregone conclusion. Others, however, consider it binding and necessitate an expiation for breaking an oath (kaffarat yamin (definition)) if it is violated. This latter opinion is more cautious. So, if you vowed to abandon a sin and then returned to it, you must perform sincere repentance and an expiation for breaking an oath. As for a doubtful vow, it holds no weight, especially for someone prone to obsessive thoughts (al-waswas). We advise you to fear Allah, abandon obsessive thoughts, and stay away from sins.