will never forget
to forget oneself―lose oneself (in admiration)―be lost (in admiration)―be absorbed (in study)―be engrossed (in one's business)―be beside oneself (with joy or grief)
お忘れなく
to be forgotten―pass out of mind―pass out of one's memory―fade from one's memory―escape one's memory―slip one's memory―fall into oblivion―be buried in oblivion
I never forget it for a moment.
ゆめ忘るな
You must not forget.
忘れないでよ。
思い出さずに
Be ever present to your mind
to forget something
the degree to which something is difficult to forget