Ex boyfriend and I argued?

1 month ago, I broke up with my ex bf of 2 years who cheated on me twice for my good friend.. They both confessed to each other when they were on a school trip tgt..

However after I found out, she didn't like him anymore & had a bf...

For 2 weeks my ex has been trying to contact me. And today we argued. His attitude was rly bad & rude. He kept defending her; saying she didn't betray me even though she confessed and stuffs. But I believe as long as she confessed & both of them were having fun tgt, it's considered as betraying me.

They both brought me to a dead end where I totally lost my confidence and esteem. I will always suffer from insomnia and have nightmares... I literally shut myself away from everywhere and social networking sites other than this.

School is starting in a week+ time. During this one mth, I managed to gain back a little bit of my esteem. But today after the argument, I felt like a lost everything about myself. He said I was being very drama about me saying they drove me to a dead end. But that's the truth, I wasn't being dramatic or what.. I literally lost everything about myself, blame myself for being stupid and ugly. I feel so shameful of myself...

I really wanna go back to school & show them as though I wasn't affected. But now it seems so tough. I'm breaking down slowly. I feel like dying. I'm so tired of all these shit...
Any advices...? Help please...?:(