I'm certain it's not Shakespeare, not unless it's been extensively paraphrased. I'm also pretty sure it's not an Irish proverb, unless it's been translated from th Irish language by an American, for the same reason: that use of "like" to mean "as if" or "as though" is normal enough in colloquial speech in England nowadays, but it's a relatively recent import from US English.

There was a nice twisted version of this that someone used to use as a sig, along the lines of:
Love like you don't need the money
Dance like you'll never be hurt
(I forget the rest but it must have involved taking further liberties with the original). Maybe it was someone here?

Marje