I feel sorry for your D. How must it feel for her to know already 2 years about the OW's and not mentioning it to you, most probably because she didn't want to hurt you.
We feel so much pain and sadness, but our children also feel that pain, after all it is their father, someone they should normally look up to.
But good for her that she opened up to you. This will definitely make her feel better, relieved.
The trip to Europe will also be something to look forward to for her. Would you be able to visit her while she there?