I agree with the previous poster about not living your life to please other people. Your daughter's MH struggles are not your fault. In fact, it's possible that living in an unhappy home with unhappy parents is no help to her at all.
You cannot shield her from life's realities. All you can do is to be the best and most supportive parent you can.
That requires that you look after your own health, happiness, and mental well-being first.
Take a deep breath and make a plan to dissolve your marriage. The no-fault process now means it's a lot easier and less conflict-driven.
Think about decluttering your possessions. Sell, chuck, donate. Make an inventory of all assets, debts, savings, pensions. Gather all your essential paperwork. Think about where you will live and what your future could look like. Start visualising how your next life phase could be.
Get counselling (alone) if you think it will help you untangle your thoughts and clear your mind.
Do not feel guilty. You have nothing to feel guilty about.
Look up FOG (fear, obligation and guilt).
Prepare yourself mentally for the divorce process, which is never easy or pleasant. But it's soon over. The you can start to rebuild.
I know it's hard with your daughter, but staying with her father is only making it harder.