Are these possible red flags? He says I’m overthinking them and that I’m ‘acting crazy’ so let me know ...

Been seeing a guy for a few months and everything has been going great but then last week he left his phone open while he was making us lunch and I noticed that he is still talking to other girls online...

I then went snooping on his Instagram and found out he follows a lot of ‘fitness girls’ and models with revealing pictures.

I wasn’t happy about it and confronted him but then he got really angry at me and was saying he can follow whoever he wants and talk to whoever he wants. I know we’re not in a relationship and that he hasn’t done anything that would make me not trust him but I said that it makes me feel insecure but he didn’t seem to care so I just left it.

Should I bring it up again? Are these possible red flags or am I overreacting?