Has anyone lost a close friend bc of a boyfriend

So recently my best friend of 4 years started dating this absolute shit head and it's just coming upto 3 months and she's decided to start having sex. But she's completely pushed me away and only cares about him and I've confronted her many times about it but she doesn't care. Wondering if I should try rebuild things or leave it and move on. Also comment if something similar has ever happened to you. P.S she is 15