expression
since then; ever since that
Refers to a point in the past after which something changed or continued. Often used when the speaker feels a clear break from a past event.
あれ以来、彼とは一度も会っていない。
I haven't seen him once since then.
あれ以来、毎日運動するようにしている。
Ever since that, I've been making sure to exercise every day.