I dont know what I should do about this!!?

I have this friend we'll call Brett so I don't give his name away and he's dating my other friemd who we'll call Aimee and they started dating in October after talking for like 2 days in my History cl. I was dating Brett in 8th grade and was happy to leave him because we are closer than close, basically brother and sister. Well, at first I was happy and I really didn't care, but now its May and ever since december, I've been getting mad and jealous and all I want is for them to break up NOW! He's been yelling at me a lot and saying no one's talking to you if I try to join into the conversation and at the table, they barely talk to me. Like in the gym, they got into an argument because Brett wouldn't kiss Aimee and Aimee got mad. My other friends all went their seperate ways totally ignoring me so I was left all alone like a loner and it hurt. It gets me so angry because now I'm seeing that Aimee treats him like a packmule, always dragging him by his arm and when he says stop, she does not stop. She gets mad at him for stupid reasons and tells me she's going to break up with him, she hits him and tells him to shut up all the time and I dont like that because i care about him more than i care about her and i want him to be treated with respect because he is such a wonderful person in every way. Aimee is a slut to be honest, putting his hands on her when she knows he is very religious and doesnt like that. They were even talking about skipping cl in the hallway, which Brett never does and thinks is bad. He's starting to change which makes him seem like the hypocrite always telling me not to change. Its just making me mad that neither of them can call me anymore or come over because they're always together. Aimee is so jealous too, he cant even put his hand on my shoulder to comfort me or anything or shell freak out like he's going to throw me down and make wild pinate to me in the hallway, Ok. It bothers me because now im getting left out and forgetten whenever shes around!! The only time we have friend to friend time is first hour when shes not there. I dont want him to get hurt or anything else. I would seriously hate Aimee if anything did. This girl is just too immature for him and to what do you call it, i need to curse but Barney bad *** SHES NOT TOUGH! Im getting mad. Ill put more on later because i need to vent!!