She's been living here for more than 8 years, but says her support system/family is in another state more than 6 1/2 hours away. I told her that she can keep the house, I just want to be able to be with my kids on a regular basis.

Note: ANY question on law needs to include your general locale as laws vary by area.

You will need to lock things down in court. You may need to file for divorce as some areas don't have laws for legal separation. So you need to have a visitation schedule, even a temporary one, in place before she leaves.