What kind of sentence structure is this: i don’t know about you, but i left my old town because of all the fighting.
why?

Compound Sentence. The sentence has two independent clauses, compound sentence. One independent clause is "I don’t know about you" and one independent clause is "but I left my old town because of all the fighting." An independent clause is a sentence that can be on itself a complete sentence.

For example. if i walk 10 feet north then go 20 feet east that would be a displacement of around 15 feet