What do you do when your best friend spends more time with her boyfriend than she does with you?

my best friend has been dating this guy for almost six months. i have no problem with her boyfriend at all as he is a nice guy. in fact i was friends with him before she was. recently she has become so obsessed with him that she chooses to hang out with him over me and at times cancels plans that we have together. i have tried to tell her that he might not be around forever and that i feel like she spends too much time with him but it has made no difference and she doesn't want to hear it. i don't think she realises that there is only so much a person can take before they begin to feel rejected and also neglected.

she is my best friend so it is a hard situation to be in as when we do get to spend time together it is really fun and i really don't want to lose her as a friend. however i am starting to feel like i put in more effort than she does and that it is unfair to me that she always chooses her boyfriend over me, when i would always do the opposite for her. i would even break my plans with others if she really needed me to and have done so in the past.

I am unsure of what to do as i don't want to lose her as a friend but at the same time i feel like the only way to get out of this situation is to slowly drift away from the friendship. please help!