It's really confusing but what do I do now?!?

[Anastasoulla]

It's maybe a big story but please read it.
I don't have a lot of friends, I am not so popular. My close friends are Stef, Kathy, Theo and Andrea. Well I feel like they've been ignoring me lately. Andrea now has got two new best friends ( my ex boyfriend and the girl who made us have a huge fight last year - but me and Andrea are "ok" now), Stef and Kathy are having fun together without me, they hangout, the meet at each other's homes, they are talking all the time about things I don't know, they are chatting on Facebook and they don't chat with me, anyway they are very close lately and they are ignoring me (they are not in love, they are just close friends). And Theo?! He is the only one who is still talking to me. But I don't know him very well, I met him last year and we became friends a few months ago. He is a good guy but we are not so close so I can't talk with him like I used to talk with my other friends! But he is the only one who still talks to me. I didn't have a fight with the others or something, I didn't even do something wrong! I don't know what's going on and I don't know what to do! I really don't want to lose my friends! What do you think I should do? Please give me advices and add a lot of details so I can understand what it's better for my friendships to do! Thanks