Final answer:
The correct tense to use is the present perfect tense: 'We have been good friends for a long time.'
Step-by-step explanation:
The correct tense to use in the given sentence is the present perfect tense. To form the present perfect tense, we use the auxiliary verb 'have' or 'has' followed by the past participle of the main verb. In this case, the sentence should be: 'We have been good friends for a long time.'
Learn more about verb tenses