I have been seeing this girl for 3 1/2 years. We have been engaged and cancelled the wedding. We have since moved into separate places and she said she needs some time to think if she sees us together for the long term. We both have kids and have to see each other often because of them. My question is I am having a hard time giving her her space... have been having sleeping and eating because she runs through my head all day long. How do I get through this time with my sanity and give her space that she wants.

There is no magic formula. It takes time. Keep busy. Do things you enjoy doing.