Best friend

Hey y'all. So I'm faced with a problem here. I:m a 16y/o female and I have a female best friend who is very important to me. We've been superclose since 2 years now. But she has recently gotten into a long distance relationship and I dont know why but its fucking with me. Its eating me up that she doesnt give me much time. I feel like we've been drifting apart. I went into depression so bad that I cut myself. No doubt her boyfriend is a really nice guy. But why is her relationship affecting me? Is this normal. Help me please:/