When am I considered single?

Based on the information provided, you have separated and therefore may enter into a new relationship. However, there are implications to introducing children to new partners, and that is something to be discussed with a family law lawyer. I presume that the 2013 or at least the 2014 income tax return is going to be filed indicating that you are separated, and that other steps have been taken to formalize the separation. As for new partners, you are at liberty to enter into a new relationship. But, again caution should be used as to the timing of when to introduce the child to your new partner. If you want to move directly into that new partner's home, and you have no other alternative, then that is what you will end up doing at some point, perhaps. You should submit your plans to your former partner as to having the child live at the new partner's home to attempt to address any concerns in that regard.