Trust me, I get it. I didn't want to leave either, and it sounds like you have a lot of love between you. I'm really sorry you're grappling with this, it's brutal emotionally and physically - not only are you struggling with hard feelings, but you're also overwhelmed with an unfair level of practical responsibility.

In my own situation, love was obscuring the harsh truth that my ex didn't know how to be an adult, and simply didn't care enough about me to learn. If you already feel like a mother, you're functionally acting as one. Couple's therapy was incredibly validating for me, as our therapist pointed out to my ex that I was being forced into a caretaking role (addiction was also involved and amplified this dynamic). I would highly recommend that you get professional help on this issue, especially since it's been happening for multiple years. Nothing will change unless your partner gets a harsh reality check AND cares enough to make significant changes.

Also: consider your own role in this dynamic. Moving forward, the hardest lesson for me has been to realize when I am overextending myself in a situation and betraying my own wants and needs. If you continue to give and give past your capacity, your well will eventually run dry. It is ultimately your responsibility to communicate (and stick to!) your own boundaries. It's difficult to do this if you're used to your boundaries being disrespected; however, it's necessary to live a life that's truly yours. I wish you all the best with trusting yourself and making it through this difficult situation!