What Do I Do When I feel Like I'm Losing My Friends?

Okay, so there's this girl. I've known her since I was about 8. I had a friend. They went to the same private school. She (my friend) started hanging out with the other girl more than me. Even though we knew each other for, like, 2 years. My friend started drifting away from me when the other girl started to come over a lot. They'd call each other a lot and my time with N started growing scarcer. Now that N's moving to Texas, M did something stupid and got kicked out if her private school. Now she sits with my 8th grade friend on the bus. I didn't sit with J this morning cuz she wasn't on. Then, in the afternoon, J sat with M. This's been going on for about a week or 2 now. They're even considering doing a web show (SHE ALREADY DID THAT WITH N!) and it's starting to get on my nerves. I almost cried today on the bus. J didn't even look over at me once. Not that I noticed, anyways. J's really nice to everyone. Almost everyone. Now M's stolen my friend again. It's pissing me off, and I don't know what to do. I told my mom, and she said, "Well doesn't she have a knack for stealing your friends?" I know I shouldn't be that mad, but now I sit alone on the bus. She also gives J a look when I sit with her in the mornings. I don't know what to do.