It's a rare honor of the highest echelon for an INTJ to say they need you. The level of difficulty that has to be overcome for one to do this is immense.<<haha true, I've never told anyone "I need you.
Introverts tend to get their energy from within, so being with people is draining. After a day filled with people or activities, introverts tend to feel exhausted and empty. They just need quiet time to come back to themselves.