My best friend ignores me after getting into a relationship?

My guy best friend of 4 years has changed. We live in different states, but we text and call each other every day, and talk about everything with each other from our problems to funny inside jokes. Ever since he got a gf this Christmas, I’ve noticed he doesn’t make the effort in our friendship anymore. I barely get one text message once a month. I just don’t think our friendship matters anymore to him. And I have lost the one person I thought I could talk to. What should I do?