Am I jealous terrible friend?

In about 3rd grade or so, I've met this girl, we've became fast friends, but she already had about 5 or 6 other friends who were 'jealous', we had so many problems because of their jealousy and kept having to see the guidance counselor and missed a lot of cl time, then in 4th grade and years later after that, she ignored me. Until this year when everyone else except for one of her friends transfered, she's crawling back to me, and I'm in a different cl then her. (Same grade, different homerooms) Then this other girl, who made other friends and only talks to her sometimes, (barely) is her "new best friend," even when I'm the one who hangs out with her, to keep her happy! She says she doesn't want me to feel like a third wheel, and of course I lie and say I don't. I do, I'm just too polite to say so; she keeps inviting the other girl to her house, to sleepover, and call her; etc, when I never even had a sleepover! (I know, I'm sad.. XD lol)