I think that rather than stepping back, if he wants to have a chance at a future with her, he needs to become a supportive friend she can count on. Right now there's just no mending the relationship aspect. But he could at least work on trying to become a friend to her to the point they can share interests and plights. Showing support through actions is probably the only way to gain back some of her trust.

I feel like their relationship can only properly start over after FL leaves and they spend at least a few years apart from each other. FL can take that time to forget about him for once in her life and see what's out there, while ML needs to grow tf up, mature and work on his communication skills. Then it'd be an actual clean slate restart, and honestly that's all I expect bc no way will the author do a 180 and pull another ML out of their hat.