What is the ruling on one who swears to abandon a sin then falls into it, either under duress or under the influence of lust, suffering from obsessive-compulsive disorder? Is his action considered intentional or coerced? Is it from the self or from Satan? Is he required to offer expiation for his many oaths? Is fasting sufficient for them?

The treatment for obsessive thoughts (waswasah) is to disregard them and pay them no mind. There is no expiation required of you for any oaths you made or broke due to these obsessive thoughts. It is recommended to consult a trusted psychiatrist. As for the sin, repent to Allah from it every time you fall into it and do not despair of repentance. Seek Allah's help, strive in your supplications to Him, and rely on Him, for Allah continues to forgive His servant as long as he seeks His forgiveness and repents to Him. Allah has promised guidance to those who strive, "And those who strive for Us - We will surely guide them to Our ways." (29:69) Allah is Oft-Forgiving, Most Merciful, and does not close the door of repentance. Allah says, "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" (39:53)