He cheated, and now things are never going to be the same. He's "wasted the chance that he's/I've been given" by this woman he deeply cared for, by cheating.
He feels very guilty and knows things won't go back, to the way they were - "And I'm never gonna dance again, the way I danced with you" - their relationship will never be the way it was when there was trust, loyalty and noone was cheating on eachother.
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