It's fine that you use Wikipedia. But you should read the article before you use it to support your argument.
The first sentences of the article says: “Delaware is a state located in the Mid-Atlantic and/or Northeastern regions of the United States. It is bordered to the south and west by Maryland, to the northeast by New Jersey, and to the north by Pennsylvania.
This repudiates your contention that Delaware is a Southern state. Just because it had slaves did not make it a Southern state. All of the original Northern states were slave states at one time. And after they moved to a different labor system they were still Northern states.
And your contention that Delaware was a “border state” is wrong too. Delaware borders Maryland, which was an actual border state to the Southern Confederacy. Maryland never seceded; fought for the Union cause. Like all the original states north and south, Maryland was a slave state.
Apparently there is some disagreement on that subject:
The final three states to ratify the 13th amendment were: