～て以来— Ever Since Then

• 日本に来て以来、一度も故郷に帰っていない。

  Nihon ni kite irai, ichido mo kokyou ni kaette inai.

  Ever since I came to Japan, I haven't returned home even once.

  来て (て-form of 来る) + 以来 = a continuous state since that point

• 手術をして以来、体調がずっといい。

  Shujutsu o shite irai, taichou ga zutto ii.

  Ever since I had the surgery, my health has been good the whole time.

  して (て-form of する) + 以来 = ongoing situation from a past event

• 卒業以来、彼とは会っていない。

  Sotsugyou irai, kare to wa atte inai.

  I haven't seen him since graduation.

  Noun 卒業 + 以来 = 'since graduation', a fixed starting point

• ・Register: formal; the following clause usually describes a lasting state or habit up to the present.
• ・The starting event must be a single, non-repeating occurrence.
• ・Attaches to a noun directly (卒業以来) or a verb in て-form (来て以来).

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～て以来 is tested against.

• ～ないうちに — Before It Happens
• ～上(で) — After Doing / In the Process Of
• ～から～にかけて — Spanning From To
• ～際(に) — On The Occasion Of
• 最中に — Right in the Thick of It
• 次第 — The Moment It's Done
• ～ところに／～ところへ — Right At That Moment
• ～ところを — Caught In The Act