An old German love poem

I enjoy reading poetry when I am having a sentimental mood.
For this first AMD assignment, I decide to read a German love poem:

"Du bist mein, ich bin dein:
dessen sollst du gewiss sein.
Du bist verschlossen
in meinem Herzen.
Verloren ist das Schlüsselein:
du musst immer darin sein."


It is a Minnelied, whch is a lyric of a song written in the 12th Century. The word Minnelied derives from the word minne in Middle High German, which means love.

I attempted to translate the poem directly into English with the help of Google Translate:
"You are mine, I am yours:
You should be certain about it.
You are locked and sealed in my heart.
What is lost is the key of my heart:
you have to always be inside."

Phasing it finer:
"You are mine, and I am yours:
You can be certain that it is true.
My heart is where you are locked into.
Oh. The only key of my heart has already lost:
there is no longer a way out. You are now sealed inside forever."

It is simple but very lovely. I love it.