It will be hard and you'll cry and you'll miss her and you'll want her back but you will get through it. I am used to the week long visits now, but they killed when they first started.
The worst I had to endure was three weeks with no contact whatsoever. It broke my heart. But we only had to go through it once because I went back to court and had it changed.
It sounds like you are doing the right thing by putting your own apprehensions aside and buying into her excitement. I remember you saying your ex is a decent guy so I am sure she will have a lovely time and it will actually, ultimately add to her sense of confidence and esteem.
But buy some tissues and chocolate in readiness to help you get through
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