Verbs used in their perfect forms link two times. The perfect aspect is used to refer back from one point to a point in time before that

• I’ll have been her for three months
• Now my girlfriend has come out to join me
• I’d never done anything like that before

Perfect tenses can be used in the simple or continuous tenses.

• Continuous tenses focus on an event which continues or is temporary
  • I’ve been doing voluntary work all my adult life