It would be important to know what he wants to do. There are many man who have several children and do not reunite with their ex. You are correct- he would always be a father whether to one or multiple kids. His time, energy and resources would be tied to them perhaps even when they are older.
You would have to ask yourself- 1/ would sharing them with others be all right and to what extent, 2/ what future does he want to have with you? (are you wanting kids of your own and is he willing to father your kids as well) 3/ what level of commitment is he willing to invest in your relationship- what are his goals of it? 4/ is he someone you trust completely (that he won't hurt you in the long run, or are you having even 10% doubt?
Ponder on these questions and figure out where does he stand in all of this. Then, your answer will come to you in a clearer view.