A lot of people are missing the bigger picture here. From the OP it doesn't seem like this " very controlling young woman," did any of this behind her partners back. Again if the "curt message," was sent to her with the knowledge and consent of her very own son, then everything else including the timeline in years, his previous consent etc., now becomes completely irrelevant - for his consent only means that he's on his partners side and is agreeing with her stance (and NOT yours) in all of this. This unfortunately places you are on the loosing end.
You're 20+ year friendship vs, a relationship with your son and grandchild, which is most important to you? - pick your priorities wisely.
A simple and genuine apology won't kill you for from your post it seems that you resent his partner for spending time with her family. Don't pick a fight with the mother of his children, it'll most likely work against you. Also, when you find yourself in a position where you're fighting more and more with your sons immediate family, as opposed to playing a loving and supportive role, (as expected of a grandparent) then you need to step back and reflect on your overall expectations as a grandparent.
I'm curious to know what your sons response was when you told him how upset you were. Not sure why people get into power struggles over such issues. It is so hard to RESPECT other people? If you insist on having your way, what will you do when they move again and don't provide you with their new address? As it is you already revealed that none of your relatives even have their address, which comes across as a red flag on your side. If you don't voluntarily leave them alone, they will take measures to make you leave them alone. Let go of your anger and reevaluate your approach before they do it for you.