BALANCING RELATIONSHIPS! PLEASE HELP ME!!!

Hey ladies. So I will explain my situation. My best friend had been in a relationship for about 2 and a half years and I've been through over a year of third wheeling and putting up with them and stuff with no problem. Just over 6 months ago I got a boyfriend and since then my best friend has been distancing herself and saying I'm the one ignoring her? I try to keep them both a big part of my life but every time one is happy the other is upset and I can never seem to keep both of them happy and I'm so over it I don't know what to do. Can someone please help, this is making me mentally unstable I've tried talking to both of them but nothing is working and I leave time for both of them and everything but I'm just so over it.