Sorry you are going through this, sort of.
You can try to look at this as an opportunity.
You've been unhappy, and now are being given the opportunity to be happy!
Make lists. Things you want to do in life. Books you want to read.
Things you can do with your daughter. And do them!
Are you still going to school? If not, make plans with co-workers after work or on the weekends. Look up single parents groups in your area.
Go to the gym, take up hiking or walking, tennis, golf, anything that keeps you moving. It does wonders for your feelings.
Let people know you are separated. You'd be surprised how many male acquantances will invite you out.
Playing music when you are alone also helps. So does meditation \ visualizations. If you feel yourself getting down with your own thoughts, picture yourself walking away from the dark cloud, or climbing up and away from it, into the sunshine.
Make it a habit to start your day thinking about what you are grateful for. Make a list of what is "good" about where you are now, and read it every day.
And talk to your friends here