"She thinks she's gonna have a party and not invite me?
Who does she think she is?"
Just because you have a boyfriend, never assume they are invited. This applies to any event or social gathering!
In my group of college friends, the boyfriends are always assumed to be invited. In fact every email we send around about setting up something always ends with- as usual all friends and boyfriends welcomed. I was talking to another friend about this and she thought it was the strangest thing. In her group of college friends, the boyfriends (and husbands) are never assumed to be invited (tough crowd). Yes, boyfriends are always invited, but like I said, they are INVITED.
This of course goes for weddings. All too often people assume their boyfriend of the week will be invited to the wedding. Never assume that and more importantly, don't be offended when they aren't. Many times the couple getting married is actually paying for their own wedding. Cutting down on plus ones is a great way to control the expenses. The only time you can expect your boyfriend to be invited is if you are living together.
Be mindful of how invitations are addressed and remember to not take this personally.