Returning to Allah and what I noticed

Assalamu alaikum, brothers and sisters. I'm really struggling with my connection to Allah and I need some guidance. I feel so ashamed to even turn to Him because I've broken so many promises-I'd vow not to do something at night and then do it the next day. I haven't been praying consistently, and when I do, it's only when I feel a burst of motivation, which makes my salah feel hollow. I've forgotten Surah Yaseen, the 30th juz, and Surah Mulk. I'm in a haram relationship with a girl, and part of me loves her, but I know it's wrong and I'm torn. Since I drifted from Allah, everything has gone downhill: I've become lazy, my grades have dropped from top of the class to the bottom, and my mental health is at its worst. I look at the students who excel-they're the ones praying sunnah at school, always close to Allah. I think that's why they're doing well. I want to be sincere, but I keep messing up. I'm tired of making promises to Allah and then breaking them, feeling like He sees me as insincere. It hurts because I truly want to change. Please, I need advice.