Hi M.,
I think you should think of these to relationships in separate instances. It sounds to me like you are saying because of the X, I can leave the current husband. If the X never contacted you, would you still have these feelings/questions that you could leave your current husband.
It is important that your daughter have a relationship with her father, but I have a question...why would a grown man allow his father to hold back information like a telephone number and address to contact his own daughter? That really baffles me. You have to realize, provided the father is still alive, he could get in the middle of the relationship again. Either the X allows the father to control his life, or he has made that his excuse as to why he never contacted his daughter.
If this were me, I would approach this relationship very carefully. Your daughter will have to break ties with her stepfather, whether they are close or not. Then she has to get to know her real father. Sure she is excited, but she still has to get to know him. And when all that goes well, then you can reunite with him if it is all right with the both of you. It sounds like you are very eager to get back together with your x, but your feelings are not the only one involved. Further, after 10 years apart, what has changed in his life? What baggage does he bring to the table? Is that all something you can work through?
Once you are back together with the X, what are your expectations of this relationship? You realize there are good things and bad things in every relationships. You sound pretty excited to get back to all those good things, but the reality is no relationship is an everyday walk in the park.
I wish you the best, but please think this one through and move slowly.