Couples and their ex - is it ok?

[me]

On one hand it sounds like she might still have a little crush on him, on the other hand it sounds like you're just paranoid. Hard to tell which one is the actual problem. Maybe it's both.

She shouldn't be liking all his instagram photos, that's a bad sign. Maybe she's doing it to make you jealous? Do you like other girls' photos on instagram? It may have been a reaction to get back at you if so.

I would just ask her straight up if she still has feelings. She might, but sometimes girls come across as flirty when they really do not feel anything romantic towards the person

And meanwhile, stop going through her things. I would have dumped you for even looking without asking permission. Is there really nothing at all on your phone that she'd be bothered by? Maybe a text or two she might misinterpret? Because you might be the one misinterpreting things in this case, how stupid will you feel then?