Do you really believe the things you’ve typed below? I can understand why you feel trapped if you do, but they’re not concrete facts holding you down. Worth thinking about:
“basically came into the relationship with nothing”
I bet you brought loads. You’ve positioned him as a saviour you’re so grateful for. You may be kind, imaginative, fun, caring or adventurous. You put a lot of effort and skill into maintaining a warm, clean home that’s welcoming for your family. This is something.
”We want for nothing”
Perhaps materially, but what about emotionally? Your daughters deserve a childhood with an emotionally happy mum. You know how much kids depend and feed on their parents emotional state, if you can’t live with your brain whilst being in this relationship they probably feel the fact too, as well as a father figure who doesn’t engage with them at all.
”my life would be nothing without him”
Not true. You have two daughters. You have all you bring to a home.
”my girls are living in a stable home”
It’s not emotionally stable.
“my children are so happy here”
Are they? Children learn to pretend and go along with their parents. You may be very surprised to hear and see how much happier they are once you leave.
”I'll leave with nothing”
Not true. Perhaps you cannot see what you will be leaving with, it may look like you would be going to nothing but there is something. And you’re not the same person as you were at 20yo, a very young woman, 6 years later you have more experience, options and knowledge.
“the life they have now I won't be able to give them if I leave.”
You can provide a different, happier, more fulfilling life. The most important and healthy provision for your children is an emotionally happy mum.
Be easy on yourself. You are 17yo, a child, when you had a baby with an abusive partner. That takes time to recover from. At 20yo you had 2 children and craved material stability. I can see how that would still be at the forefront of your mind. You can provide a better life for your children and you do not need a partner to do that.