well 10 years is a long time....it's what you know. it might be miserable, but it's YOUR miserable. life without this relationship is going to be different and right now you don't know what that different looks like.
it's kind of like Let's Make A Deal - you don't know what is behind Curtain #1.
but if you just take that brave step, cut the ties, and get free - it WILL be better. maybe not the next day, change takes time. but you will make room in your life for so many good things. just let go of the big BAD thing. you can work on forgiveness as time goes by. that too is a process.