You might want to check with your lawyer to be certain, but as far as I know, once you are separated (especially with a legal document), you are free to date or do anything you want to short of actually marrying someone. I lived with people during the separations preceding both of my divorces being final.
Obviously you aren't rushing into anything like that, but I don't believe you are doing anything legally or morally improper when you have a legal separation and a pending divorce.