my partner of four years (19F) just broke up with me (21M) out of the blue

Me and my partner have been together for four years. We have had some really difficult conversations and we’ve both done things we regret in the relationship, but we have always been committed to making it better and we have, at the end of the day, always been able to talk things through. A recent argument we had that seemed to me to be resolved affected her more than I thought, and she broke things off really suddenly a week after. We have always been able to talk things out and we’ve made it out stronger from much worse situations, and I’m confident that our relationship is able to be repaired. I feel like I was truly blindsided by this and if we could both come to the table now that I’ve had time to think, we could mend this and be even better off than before. It’s been two days, and I don’t know what to do. Every bone in my body is screaming for me to fight to save this relationship because we love each other so deeply and complement each other so well. I just don’t know why this was so different.

How do I go forward?