How would the end of slavery in the south have affected the confederates ability to fight the civil war?

Slavery was not ended until the 13th Amendment of December 1865.

The Emancipation Proclamation made it illegal, but Congress had no power over the Southern states at that time.

The Proclamation affected the Southern war-effort because Union troops were licensed to free any slaves they came across in their Southern campaigns. This robbed Southern employers of much of their workforce, and certainly affected the Confederate war-effort.

Only in the last few weeks of the war did the Confederacy approach the British and French, offering to end slavery in exchange for their support of a separate sovereign nation. The offer was refused, to nobody's surprise.