In all fairness, what you do is up to you and should be your choice. It is not my place to suggest you do or do not contact X1. That's not a back peddle, it is simply a reality.
So in the end, this is simply food for thought. Maybe something to act on if you so choose and maybe something that you just think about and then keep moving forward.
And that goes both with X1 AND X2. Because this is YOUR journey.
Again, that said, as I mentioned earlier, perhaps you are simply attempting to rescue X1 by leaving her alone. Yet in reality, perhaps she is adult enough, mature enough, stable enough in her own mind to deal with what ever you might have to say to her.
That... should be HER choice... whereas right now, you are worried about protecting her new life... she might not respond at all... she might thank you for letting her know... who knows...?
Again... this is all food for thought. At this time, I don't think you should do ANYTHING about these thoughts. Just sit on them... Eventually... you will do what you do and it will be right for you. And that, again, might simply be you mulling this all over and moving forward with your life.