I'm grateful for all you have done, but I'm sorry because I'm not strong enough to keep doing this. It's just constant heartache and pain and resentment. I have been sober for nearly three years and the "happy, joyous and free" they often mention in recovery is not something I can ever have. I don't want to keep going on anymore because the hurt never stops.
"The strongest among us are the ones whose courage let them speak about their own troubles and struggles. You can see the weak hide, but the strong often speaks." - Me, I guess
"Happy, joyous and free" sounded like someone was trying to sell you something or cheer you up. Regardless, I cannot really give you anything to inspire you to keep going. What can I do? I don't want to keep going on, either. All I know is that you have been putting a lot of efforts to live through another workday and another toxic person. That is a something worth celebrating and remembering.
Giving yourself another chance is not a mistake. It's like taking a deep breath before diving into the deepest point of the Mariana Trench. Everyone knows it's hard and painful so there is no need to feel sorry for not being able to complete it.
We can talk to you as much as you need but I think you need professional help.