Speaking from experience I think it's about him feeling that she deserves to be with someone else but not wanting to lose her.
He feels his anxiety ("I chew on the bones of the day while you sleep soft and warm in the night"), low self-esteem ("I wonder if you look at me and instead see him taking my place") and depression ("alone at the end of the day I just sit with my head in my hands") is "holding [her] down," when in reality she could be perfectly content with the relationship.
Speaking from experience I think it's about him feeling that she deserves to be with someone else but not wanting to lose her.
He feels his anxiety ("I chew on the bones of the day while you sleep soft and warm in the night"), low self-esteem ("I wonder if you look at me and instead see him taking my place") and depression ("alone at the end of the day I just sit with my head in my hands") is "holding [her] down," when in reality she could be perfectly content with the relationship.