You give an inch, she will take a mile. You got married to be with this person for life not to take mini breaks when the feeling hits her. Set your boundary: You can not be in a marriage where a third person is involved and stand firm. Tell her that you are sorry that she feels this way but this is not what marriage is about. You are not a safety net.
She may be 80% sure she will be back but I am 100% sure you would be gone.
Keep posting.
kat
Me-53(and learning!) S24, S21, D18, D17 Just keep swimming, Just keep swimming. Dory