What is the solution to the problem of falling into watching pornography and masturbation when alone, despite trying to commit to lowering the gaze and good behavior outside the home, and feeling hypocritical as a result?

All of humanity errs, and the best of those who err are those who repent. Your feeling of shortcoming and fear is commendable. Make this fear productive through sincere repentance and righteous deeds. Repent to Allah immediately, and remember the harms and afflictions of sins. Read the book "Ad-Dā’ wa ad-Dawā’" (The Disease and the Cure) by Ibn Al-Qayyim. Accompany the righteous, minimize sitting alone, and increase your remembrance of Allah (dhikr), supplication (du'a), recitation and contemplation of the Quran. Reflect on the names of Allah, death, and what comes after it. If you stumble and return to sin, do not despair. Rather, repent again until Allah grants you sincere repentance, after which you will not return to sin.