Struggling with Intense Feelings in a Healthy Relationship

I love my girlfriend and we've established healthy boundaries. She needs time and days to herself to recenter. I think I need them, too. I struggle on days and nights off with intense feelings that the relationship is over and that this time off is the last. I feel valuable and worthwhile when I'm alone and single. I feel valuable and worthwhile in the relationship with her. Why do I feel so bad when I'm in the relationship but alone? It's easier with medicine in me but the feelings are still there. I know the source is either my traumatic relationship with my ex or my mother.