Girlfriend going to a concert with a guy? Is that cool?

MyExperience
So my girlfriend of 8 years with some huge ups and downs (she has a drinking problem and turns violent) wanted to go to a major country concert a couple hours away. When I said I wasn't into it, she posted on FB that she was looking to go if someone had any extra tix avail and is fun at concerts. She told me that her friend from HS reached out and invited her (he bought two Tix but recently broke up with his gf) when I told her it bothered me she said "it's the same as when you go to things where all these young girls in bikinis are at without me" referring to when I hang at the beach with my buddies and their wives and wives younger sisters while my girlfriend is working.
Also, she changed her FB settings so I can't even see her friends unless they are mutual friends. Says she doesn't know how to fix it.
Before she confirmed this concert date I invited her to a different local concert for the night before and now I'm not even sure I want to take her.
Should I be concerned?
Happy to provide more info if you need it.
Thanks.
It's no big deal he's just a friend
It's a big deal but just trust her.
It's a big deal break up now
Other (explain)
Select gender and age to cast your vote:
Updates
+1 y
Also, should I still take her to the other concert the night before her "date"?
Updates
+1 y
Since our argument about it this morning, I've not responded to her calls or texts but now she's being all lovey dovey texting me about wanting me (sex) tomorrow night. What's up with that?
Girlfriend going to a concert with a guy? Is that cool?
27 Opinion