My boyfriend of 5 years left the state without telling me: red flag or no?

Today is 4th of July in America and my boyfriend said he was going to a beach that’s less than an hour away with his friends (all men) for a guys day to celebrate just for the day. I didn’t ask to come, I was not invited, so I made my own plans with my girl friends for girls-only time.

When he texted me today he said he was in another state that is known for partying hard and staying until Thursday and it’s not just the guys, one of them brought his girlfriend.

Am I overreacting for thinking this is odd behavior? If he had just told me beforehand, I wouldn’t have cared, like have fun, but it seems like a communication issue that could’ve been so easily avoided had he just mentioned it.

I am unsure of how to approach this situation.
My boyfriend of 5 years left the state without telling me: red flag or no?
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