I don't think you can make any hard and fast rules for this. Maybe in a lot of situations, the new person is a just a "transitional" relationship, and you should save yourself the heartache.
But every situation is different. In my case, my ex and I had been separated for a year and a half when I met DH. It wasn't a situation where there was even a remote chance that we would get back together. But we were both emotionally wrung out from the process of actually separating and all the pain that that involved, that neither one of us had the "stomach" to go through the legal process. Maybe we were just procrastinating, I don't know, but I remember that I felt I could face the pain of the actual "paper" process, and felt that it wouldn't hurt anything, or change anything to wait a while.
And in our case, we actually were "friends" by the time we did go to court and make it legal, so it worked out okay. I know that this is probably the exception to the rule, but if my DH had taken the line of not dating a separated person, who knows how things would have turned out.
But every situation is different. In my case, my ex and I had been separated for a year and a half when I met DH. It wasn't a situation where there was even a remote chance that we would get back together. But we were both emotionally wrung out from the process of actually separating and all the pain that that involved, that neither one of us had the "stomach" to go through the legal process. Maybe we were just procrastinating, I don't know, but I remember that I felt I could face the pain of the actual "paper" process, and felt that it wouldn't hurt anything, or change anything to wait a while.
And in our case, we actually were "friends" by the time we did go to court and make it legal, so it worked out okay. I know that this is probably the exception to the rule, but if my DH had taken the line of not dating a separated person, who knows how things would have turned out.