How to stop wanting her:
Quit sleeping in the same bed.
Quit using the washroom when she's in it.
Quit touching/hugging/holding her.
Treat her as an administrative assistant or someone else you work with. Be professional.
Get an evening job - so when she's home with the daughter, you're out working.
Spend as little time as possible in her company - only what is needed to make the plans for your daughter.
Every time you start to think about sex with her, do something else mentally or physically . . whatever distracts you.
Have you talked to a lawyer? What are your custody options if she leaves you?
Is she supporting the household right now? If so, what are your options for making enough money to support you and your daughter without her?
And, most important, ARE YOU GOING TO LET HER WIN? If you off yourself, she wins. She will have succeeded in taking EVERYTHING, including your future, away.
There comes a time in everyone's life that they have to make a decision. Am I going to choose life or death? If you choose life, the ups and downs, the good and bad, the length of time you've been given, then you take what you've done, what's been done to you and the future possibilities and DO WHATEVER IT TAKES. You ride the hair off that horse, you refuse to LET someone else make your decisions for you, you decide that GOD DAMN IT I AM GOING TO LIVE and NO MATTER WHAT HAPPENS I'll ride this train. I'll see the sunrise over the pyramids of Egypt, run the sands of the Sahara, climb the Himalayas, kayak the fjords of Norway, "sail beyond the sunset" and live for as long as I live.
When depression strikes, you take the bull by the horns - go back to the psych, go the the doctor and get the meds to deal with it, go make some new friends, do whatever it takes to live well. After all, the best revenge is living well!
If you decide not to choose life, then eventually some 'circumstance' will come along . . and it/she/he/them will win because ALL of us deal with pain at some time. "I've been there - that's why I'm here." I've chosen life - no scum-of-the-earth is going to take MY life away from me.