It's a little hard to tell because there isn't much to go by. It seems to me that he's talking about someone that was close to him at one time. He's over this person and ready to move on. He has no desire to see him/her anymore and he's happy they aren't there in his life anymore.

It's slang for "I'm sick of this situation"

Yes, it means that the person is tired of the situation and no longer want to deal with it.

He Stopped something sooo bad

"So done with ..." es la forma en que los adolescentes de los EEUU dicen que estár harto de hacer una cosa - sobre todo las chicas. Así que en este ejemplo, la chica dice que está tan harta de echarle de menos y desear que estuviera con ella. Debe haberlo pillado con otra!