Is my girlfriend cheating on me?

My girlfriend of 8 years now has recently started going out without me on the same night every week. She claims to be going to see the same band every week in the same bar. She goes out of her way to see this band. She also comes home very drunk which is odd because before this she wasnt a big drinker(maybe 1-2 drinks a night). But when I am out with her she refuses to drink. She also gets dropped home by the same band member every night which I find strange. If it was me she would most definately have a problem with it. Anytime I bring it up she picks a fight with me. In anybodies opinion am I wrong and jumping to conclusions or is she hiding something?

I would definitely not like it. If the band member is a male then it's wrong.

Um, I'd say clearly "something" is wrong here. I'm a female and I know all about starting fights to take the heat off a subject I don't wanna talk about. She may not be cheating but she may want to. She clearly likes this person who takes her home. Let me ask this first though, does she get dolled up more on these nights without you than she does with you? That's a tell sign right there. Has she been texting or calling anyone secretly like? Sneaky I guess rather than secretly. Is your sex life any different now she's been going out? These are some things to look for. I hope ts not the case though.