Hey, in my experience boundaries are really really important, and often I looked for people to set their boundaries so I would know what mine were. But what happens when they don't have boundaries?? Emeshment. In my journey, there have been very very few with good healthy boundaries. I appreciate them the most. I learn the most from them. They are the best role models I've had, BUT it took their being just who they are, and my slowly dawning comparison with the other people that led me towards having my own health(ier) and growing EVER healthier boundaries...
I notice you focusing on him. What about focusing on yourself? Keeping yourself healthy? Saying to him, "I'm not worthless."
You reaffirm yourself, and in doing so--by being good to yourself--you demonstrate you deserve worthiness and get it by being there for him. It may take a while for him to get the message (years even). But you don't do anyone any good by being less nurturing of yourself.
Just my two cents.
P.S. I've been where he is.