I'm a jealous mess

Okay, here goes. I need to get this off my chest because I can't tell anyone I actually know. It's eating me up inside. My best friend, Sarah, is like, amazing. Everyone loves her. She's beautiful, smart, funny, and guys are always falling over themselves to talk to her. And I'm…well, I'm just me. I'm okay, I guess, but next to her, I feel so plain and boring. She just started dating this guy, Mark, and he's perfect. Seriously, perfect. He's kind, he's got a good job, he's gorgeous, and he seems totally into her. And I should be happy for her. I really, really should be. But all I feel is this ugly, twisting jealousy. It's not even that I want Mark for myself (okay, maybe a tiny part of me does, but that's not the point). It's just…why does she get everything? Why is it so easy for her? I know it's a terrible thing to feel, especially toward my best friend. I hate myself for it. I try to be happy for her, I really do, but inside I'm just screaming. I don't want to lose her friendship, but I'm scared my jealousy will ruin everything. I don't know what to do. How do I stop feeling this way?