I have a doubt in this statement:

We've been best friends for years and still we're going to be more than best friends
1)What is the simple predicate in this sentence?

This is a compound sentence; each independent clause has its own simple predicate.

Divide this into two (what could be two complete sentences). Then tell us what the verb for each clause is ... there will be TWO simple predicates.

1)been 2)going

Almost. Remember to include auxiliary verbs:

have been

are going

The auxiliary verbs are tricky when they are included in a contraction, such as We've and we're.

To identify the simple predicate in a sentence, you need to identify the main verb or action of the sentence. In this case, the main verb is "going." However, it is important to note that "going" is part of the verb phrase "going to be," which is used to express a future action. So, the simple predicate in this sentence is "going."