It's only taboo because of misguided notions from the century before last. Before that, it was generally accepted, if not somewhat encouraged in many instances. In some cultures today, it still is.
With all of this being brand new to you, (and HIM too, I bet) take this like you would any other relationship in which you would find yourself unusually falling fast. Slow it down a little, and take a deep breath, BOTH of you. You will find many stories here of how these relationships are want to get very intense, very quickly. You will find many of those, where that fact alone is as big or bigger issue than any potential "flipping of the biscuits" by family. As this part of the family has been estranged for many years, initially, it could be quite the scandal. However, if you two slow things down, keep it on the "down low," as we say, for a while, get here and get the facts, play your cards right, it COULD bring the family closer. It will not be easy, and it will take a LOT of patience and work to get there. That's a little ahead of where you are right now, but methinks you're headed that direction, or you wouldn't have found your way here.
Like I said, take a deep breath, calm down, look around, make yourself at home, and get familiar with the facts. Chat him up, tell him what's going on on your end, and see if he isn't at the same place. If he is, send him a link to this site, and this thread, and get him on the same page as well. It certainly sounds like you two have some potential, if you play this out correctly.