Does the repetition of the Two Testimonies every time the one afflicted with obsessive doubts feels disbelief make him return to Islam?

A person suffering from obsessive-compulsive disorder is excused and rewarded for their struggle against these obsessions. The beneficial cure for obsession is complete avoidance and not paying attention to it, believing that they are satanic whispers, and fighting them off.

Uttering the two declarations of faith (Shahadatayn) because you believe you have disbelieved increases the obsession. The correct approach is not to utter them in the case of doctrinal obsessions, unless uttering them is a form of dhikr (remembrance of Allah) by which hearts find peace. The sign of this is that one does not begin with them or restrict oneself to them.

The most beneficial cure for repelling obsession is to turn to the remembrance of Allah and to do so frequently. Obsession afflicts those whose faith is complete.