I came across a song, Vergiss Mein Nicht, performed by the tenor Fritz Wunderlich, famous for Mozartian roles according to Wikipedia, but this is more in the tradition of singers such as Richard Tauber. I sent a link to a friend who is very into operetta style songs - it is a shared interest! - but he wanted to know what the lyrics would be in English. He couldn't find an English version and neither could I, so I had a go with the aid of Google Translate and some tidying up. I think the original and the translation stand quite well on their own as poems, which is often true of this song genre, but not of all song lyrics of course.
I took a certain liberty in line 3, because red is not mentioned in the original, but I think it works and it helps with the rhythm of the verse.
When you're so tender
Then I think, Forget me not!
And when your red lips kiss my mouth
Then I dream, Forget me not!
When you wrap your arm around me
Then I pray, Forget me not!
And when the day comes that we part
Please, Forget me not!