My Bestfriend likes my OTHER Bestfriend?

The title may seem a bit vague, so i'll explain. Me, and my two best friends have been together since... EVER, but recently, My best friend, Justin, have been with my OTHER best friend, Marcus more often. They always seem to be happy! And I feel jealous because I am not part of their conversation. What really ticked me off was when we were both invited by Justin to come over to his house. My Mom said NO, so only Marcus went there. I went online on Facebook and I chatted with both of them. They said that they are having a good time, it was awesome in Justin's house and other **** like that. I WANTED TO BE THERE!!!!! Also, Us 3 , were HUGE Sonic fans. But again, Justin has sent some videos to Marcus about Sonic, but NOT ME! DAMNIT!!!! That really sucked, I feel like I am left out. Also, WE created this Mini-Series (drawings) about a retarded Ninja (yea, I know), and on the bottom left side of the front cover said "Created by: Marcus and Justin" WTF?!?!?!?!?!?!?!?!?!?!? What do I have to do? I can't just ask them "Hey, are you guys avoiding me!?!?!?" It would be too obvious. Are they still my friends?