I started dating someone, and my friends don't talk to me now, what's up?

About 4 months ago I started dating a guy and we've really hit it off. We have known each other for a while, and my 2 best friends have known him even longer than me. We've all always thought he was a great guy. So I understand that a lot of the time girls distance themselves from their girl friends when they begin a new relationship, but I haven't done that. I reach out to my girls all the time and especially my best friend, she never wants to get together anymore. When we do, she is disinterested, and out right rude to me. And no, I don't talk about my boyfriend to her that much because I feel it will only make it worse. What's up with this? Why are my friends becoming so distant when I really do try to make time for everyone who is important to me? We are in our mid 20's so I really don't get it.