More literal translations:
* Je t'aime, au revoir. (I love you, goodbye.) - This is the most straightforward way to say it.
* Je t'aime, et je vais te manquer. (I love you, and I'm going to miss you.)
More poetic or metaphorical translations:
* Je garderai toujours ton souvenir. (I will always keep your memory.)
* Notre adieu est un au revoir. (Our goodbye is a farewell.)
* Je t'aime, même à distance. (I love you, even from afar.)
The best way to say "I love goodbye" in French depends on the context and the specific emotion you want to convey.