Identify sentence as simple, compound, complex, or compound complex
“its proprietor, roderick usher, had been one of my boon companions in boyhood, but many years had elapsed since our last meeting”
also, which part is the dependent clause and independent clause of the sentence?

Compound sentence.

Explanation:

A compound sentence contains at least two independent clauses (with no dependent ones; if there is a dependent clause included, then it is a compound-complex sentence). There are two independent clauses in the sentence above: Its proprietor, Roderick usher, had been one of my boon companions in boyhood AND but many years had elapsed since our last meeting.

There are no dependent clauses here - both clauses are independent and can exist on their own.