You believe it is essential to keep the country together. Though you have won the election decisively over three other candidates, you resign immediately. You have become the issue, and perhaps the horrors of civil war can be averted if you remove yourself as a point of contention. The personal sacrifice and disregard for the will of the electorate will be worth it, if just one life is saved. You work out some kind of autonomous rule arrangement through negotiations, allowing the secessionist half of the country to keep all of its institutions, no matter how morally repugnant this may be.
Nothing is worth losing thousands of lives and plunging into the agony of civil war.
You insist that the country must stay together. You commit all the nations's resources and your leadership abilities to making sure that it does. You accept no compromise on your election as President. To do so could threaten future election results, setting a dangerous precedent by rewarding threats of secession. The main point of the conflict is an immoral institution that must inevitably end.