You actually seem to be putting so much thought into this. Good on you though for considering the kid so much, I'm sure most people would be far more selfish than that.
Also.. Not every relationship will last. And you don't really know yet whether this is to last. But, even if it doesn't, I'd say it's him that should decide whether to let his child know, and therefore decide whether a break-up would be too difficult. And it's not really a good enough reason to not be with him!
You seem to be thinking about this too hard, but I suppose the best thing to do would be to talk it over with him.