Ever since my best friend got a boyfriend...?

sad but true this happens all the time.as you get older this does usually change a bit.not a lot you can do to change this,it's not so much that she doesn't care any more,she's just wrapped up in her "new love".tell her calmly how you and the others are feeling,wish her happy birthday and just wait and see what happens.it's possible you may have to wait a good few years till she realizes that boyfriends come and go but that women Friends can last a lifetime and you need their shoulders to cry on,their ears to listen to you when the men get really shitty! try not to let this take over your life,get out there meet other people and try to enjoy life.