Why does he get away w/ S***?

My ex was sent to jail last month for stabbing a man 3 times in the back while he and the other man were drunk. He got charged w/ criminal possesion of a weapon and felony ualt /criminal contempt cl B. I guess the guy who got stabbed said he was trying to throw him down the stairs and thats why he stabbed him, so I guess he will get off. Less then every 6 months he gets arrested and sent to jail, its like clockwork. This is his 3-4 felony. He gets it lowered EVERY darn time. He has bipolar. He uses that as an excuse. When the hell are they going to send him to PRISON and keep him there? When he actually kills someone? And his arrests are always for violance