Does departing from Islam occur by repeating ablution, prayer, or recitation, despite having taken an oath (I swear by Allah that if I repeat ablution, then I am among the disbelievers) to rid oneself of obsessive-compulsive disorder? And what is the way to get rid of these doubts and obsessions?

One must not pay attention to the whispers of Satan. Their cure lies in seeking refuge with Allah from the accursed Satan, and continuing in worship and supplication, for doubt does not invalidate worship.

As for swearing by exiting the religion, it is an oath of prevention and requires expiation. It does not lead to apostasy if one did not intend disbelief. An expiation for breaking an oath is required, along with repentance and seeking forgiveness.