Dating after separation but before filing for divorce is not advised. In fact, some states adultery is grounds for divorce. However, your situation is different - you have already filed. As a general rule, once a divorce is filed, there is no issue as to adultery. The filing is deemed a "date certain" that the marriage is in the process of being dissolved.  Basically, this means that the court will assume that at the point the filing meant that as far as the parties were concerned the marriage was really over and the they were moving on their separate ways.That having been said, in your case you are not simply dating you are co-habitating. This can make negotiations and settlement a bit more complicated and adversarial.  Additionally, in some states co-habitation can affect the determination of if, and how much, alimony should be granted. It can also factor into custody/child support considerations.