It's unnatural. It's not the efforts themselves that will "cling to you". It's the memory or the fact of those efforts. Even so, I find the use of the word "cling" unnatural there.
Also, "completely impossible" is tautologous (even though you'll hear it a lot). Something is either impossible or it's not.
I would say something like "It's impossible for me to forget your efforts - the memory/those memories will be with me forever".
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