以来

1. Origins, structure, and basic meaning

• Structure: 以来(いらい) marks a continuing period starting from a particular time.
• Basic usage: It describes not having met someone since graduation or a habit maintained since a certain day.

2. Common pitfalls and similar expressions

• Continuity compared with 以降
  • 以降(いこう) marks the range from a given time onward and can also refer to future schedules. 以来 emphasizes a state or repeated action continuing from a past starting point.