“I had been waiting for you since morning.”The past perfect continuous tense is used to describe an action that began in the past and continued up until another point in the past. In this case, the waiting started in the morning and continued until the time being referred to in the past.The structure of the past perfect continuous tense is:had + been + verb-ing So in this sentence:

• “had” is the past perfect auxiliary verb
• “been” is the past participle of “be”
• “waiting” is the present participle of the main verb “wait”

This tense emphasizes the duration of the action leading up to a specific point in the past. The phrase “since morning” provides the starting point for the waiting.