Seeking Guidance on Maintaining Boundaries

Salam everyone, I'm a student reaching out for some advice. I've met a sister at my school whom I deeply care about, and we've developed strong feelings for each other. From the beginning, I've tried to set clear limits, expressing that my intention is marriage in a halal way. However, we ended up spending a lot of time together, talking late, and unfortunately, we fell into zina. The guilt is overwhelming, and even though I regret it, I struggle to stay away. I was raised Muslim but wasn't very practicing, having grown up with many Western influences. Lately, I've been striving to improve my deen and become a better Muslim man. It's just so frustrating-I feel like I'm failing and it's starting to affect my mood. I don't know how to break this cycle and would truly value any supportive words or steps to help me get back on track.