best friends n boyfriends

my best friend of five years has had her first real boyfriend now since like june and i honestly couldn't be happier for her and it is nice to see her happy with this dude....
however she's now always with him and i never see her. we used to always do stuff like sleepovers n go out to town n that but now, whenever i make an effort to make plans with her she's always with her boyfriend and i feel really replaced. i really don't expect her to devote all her time and attention to me because that's just selfish. 
i've told her this before and she says she doesn't want to me to feel this way and she is sorry but it just keeps on happening. this may sound really mean but if they break up, i'm the one going to be there for her through thick and thin at the end of the day, not this guy. 
not a bashing post, i truly love my best friend and ill always be there for her but recently i'm feeling really shunned to the side. 
any tips on what i should do ?