How to stay committed to no contact before marriage after overcoming a past mistake

Assalamu alaikum, brothers and sisters. My fiancée and I spent over a year in a relationship that wasn't halal, and we've now both decided to stop all contact until our nikkah. The problem is, I've already broken this commitment a few times, and we're trying to restart it again with a fresh promise. As a brother, how do I stick to this sincerely without constantly stressing that she might lose feelings for me? I'm really struggling to handle these doubts and stay strong.