Im in love with my ex, but his twin brother is in love with me, but i dont love him bak?

Sounds like a soap opera. I can't believe you're only 13 and this type of thing is going on! I would tell him about how he's being cheated on, but I wouldn't try to get back together with him. Try to get over him and become good friends. I know it's hard, but you're going to have to get used to it as you get older. As for his twin brother, I would also try to become friends with him.