I can't really come up with a definite technique for this specific quote, and there's probably someone else who would have a really good technique for this, but there are five ways I've interpreted it as:
-Emotional Language that evokes the imagery of tragic love fleeting away...
-Repetition of Love -- maybe shows signs of regret and hesitation in leaving this love? This one is a stretch QwQ
-1st Person in "If e'er I loved her..." (Not sure what the effect here would be...)
-Juxtaposition; with contrast between the past loved and the present love suggesting that love is in a dynamic state...
-Maybe even Hyperbole, because love can't truly disappear...?
I'm sorry if these don't help you at all and that they're completely wrong interpretations! What's this quote from anyway?