They broke off because there is no agreement among the three options.
The first option was that Salva Kiir allow Riek Machar to become vice-president, and the government objected to that.
The second option, which was brought by the mediators, IGAD, said they should reinstate Riek Machar as the prime minister, and that the two vice-presidents must be appointed by the president. The opposition objected.
The third option was about security. There are two security forces. One is the army under Riek Machar, which would be under his control for a period of three years, and the government of South Sudan would have its own army for three years. The government of South Sudan said no; Riek Machar should only have control of his army for a period of two months.
Then there's the issue of the federal system. The government agreed, but the details were not discussed.