No, you are absolutely not being ridiculous. She sounds very self absorbed and narcissistic and she's harvesting IG for attention. She's concealing you by not uploading a photo, thinking it might interfere with the comments she gets from thirsty guys and probably DM's. You've caught her on one instance but her phone is full of DM's from other men and she has probably cheated on you already, on numerous times. You can guarantee she did on this trip.

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Save yourself the additional anguish, anxiety, doubts and gaslighting and end it ASAP. She won't change, it will only get worse. When you end, no contact and try to move on emotionally. Best of luck.