How long should me and my girl friend wait to live together?we both have kids from before...

Until you are married to each other?

Finish what you need to do and that is raising your kids. You can always see the honey on the side when the children are with the ex or grandma or grandpa. They need to come first. Do not bring a honey into the relationship with her/his kids. You have enough to deal with. I know. I come from experience. When the youngest is 18 then you can plan your next stage in life. Marriage.