When you're in love with someone, everything in your life changes. You don't see your friends and family as much because you're spending a huge chunk of your time with your boyfriend. Everyone says you seem happier, like you're floating on air. Everything that comes out of your mouth starts with his name ("John thinks..."). It's like your whole life suddenly revolves around this guy.
What if it's not you that's in love, but your best friend? You remember her, right? You used to hang out all of the time and go shopping and watch movies—what's her name again? Now she has this AWESOME boyfriend, who's SO much fun (you're rolling your eyes now, right?), and you never see her anymore.
Whenever a friend gets a boyfriend, the process starts off slowly. First she's gushing about him to you on your nightly phone calls. Then they're "official," and she never stops talking about him. So much so, that you start discussing the weather or golf—anything to bring the subject off of how gosh darn fabulous he is! The girl you used to hang out with every weekend is breaking your plans left and right.
It really hurts when you feel like you've lost your best friend to a dumb guy. You rely on her for good times, a shoulder to lean on, someone you can spill your secrets and dreams to, and now it seems like she doesn't even need you!
You need to sit your friend down and tell her how you really feel. You feel left out and forgotten, and you owe it to yourself to be honest with her.
Don't try to drop by her house or corner her in the hallway at school. Call her a couple days before (so she can clear her schedule with WhatsHisFace) and ask her if you could meet her somewhere to talk. Pick some place quiet like your house or a coffee shop. Sit down and tell the truth!
Before you meet up with her, sit down and list all of the reasons you're upset. Be realistic. You're upset she doesn't involve you in her life anymore, not because you think her boyfriend's a total dweeb. Don't bash him, because that will only turn her away from you. She'll be less apt to listen if you're talking smack about the person who is most important in her life right now.
Most likely, she'll realize how poorly she's been treating you and apologize. You still may not see her as often as in the pre-boyfriend era. You have to realize that she now has TWO very important people in her life.
If she acts completely unresponsive to your feelings, don't give up on her. She'll come around eventually and realize hanging out with her boyfriend every single waking moment is incomparable to what you two have. If they end up breaking up, save the "I told you so." Be there for her. That's what real friends are for!