Is he cheating? What should I do?

I (21F) and my boyfriend (26M) have been dating for a couple months. LDR, see each other twice/month. He’s the one who asked me out despite my initial hesitation for “moving to fast”. But he just claimed he loved me too much and he just knew he wants as much of me as possible.

I looked through his Instagram posts and see there’s a girl recently commenting daddy on his photos and then he deletes it. However, on his last post he replied flirty to her and they had some banter. Seems like this would only happen between them if they were close.

It made me super paranoid all day and obviously I start texting different. So I decide to confront him that afternoon through a text… he doesn’t open it for hours (until 2AM). I then call him 5 times with no reply.

Should I call him again? Is it reasonable to call him at 3am for this? think he just broke our trust. how should I approach this? And could he be cheating?

Is he cheating? What should I do?
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