I can tell you from my experience that the bdad of my son would want to know. He also has other children but I feel confident in saying.... He would want to know.
That said, I would have some 'splaining to do
The man I am with now would also want to know. We have talked about this "what if" situation. He would be surprised (and have some questions of course) but he would want to know.
Also with the bdad of my son, I don't believe me or the fact that he had a son out there ever put a strain on his marriage. He may have told her early on (I dont know). I don't think that should be a concern. Even if it is.... You will be telling him. Not his wife or kids.
I would contact. You will never know if you dont try... hehehe I say that having asked the same question 3 months ago (should I contact my son).
Totally get the insecurity.... ((Hugs))