Struggling with deep feelings of despair

Assalamualaikum everyone. I'm dealing with a really tough battle against haram habits that started when I was young, from watching inappropriate content online to seeking out sinful acts in person. Alhamdulillah, I haven’t engaged with those major sins for over three years now, partly because I involved my mother to help monitor my spending-so she'd know if I ever tried to go back to that. Even now, though, I often find myself browsing through tempting ads and struggling with impure thoughts, barely making it a week without slipping up. Yet, I’m so grateful to Allah for protecting my health through all this. I truly love Allah, enjoy reading the Quran, and find peace in remembering His attributes, but when urges hit, all thoughts of accountability just vanish. It feels like my relapse rate stays the same no matter what-whether it’s Ramadan, after prayer, or any other time. Finishing the Quran hasn’t eased the struggle either, which sometimes makes me wonder if I’ve lost His mercy. My mind gets tangled in questions too: How can Allah be both severe in punishment and the Most Merciful? How do free will and His decree fit together? If everything happens by His will, why am I held responsible? It’s a cycle that leaves me feeling lost and hopeless. Why am I sharing this? Because I’ve reached a point where hope feels gone. I know Allah doesn’t make mistakes, and He created me for a reason, but I can’t see what it is. Sometimes, I even wish I wasn’t created or could just end things, but I know that’s not the way and that suicide leads to Hell-so I won’t act on it. What’s wrong with me? Is it a lack of willpower? Allah has blessed me in so many ways-with life, sustenance, and future prospects inshaAllah-yet this addiction remains untouched. If I don’t find a way to stop, I fear where these thoughts might lead. Please, any advice on how to break free?