What should I do about this friend?

[JustKindaLost]

Okay, so I have a friend, we're pretty close, but ever since the start of the school year our friendship's been in decline. We were such good friends, but now whenever I talk to them on Facebook they give one word answers or say they're busy, when we used to talk all the time. They used to message me lots per day, and now they don't at all. They say they're busy, but they're always skyping with another person... It's also the same at school; they're always with this other person and doing shenanigans, and even though we sit together in classes I just don't have that connection with them. I wanted our friendship to be closer this year, but it's gone the complete opposite way. I feel I'm being oversensitive, but I honestly feel really excluded and it makes me feel sad. I know I can make new friends, but is there any way I can reverse this decline, to restore our former friendship? :|