help with translating these two phrases

hi i really cant understand these tow phrases
i heard them while listening to certain song


君の後ろ姿さえ 明日への希望に思えた日を
幻にしないように 瞼へと刻んだサヨナラ

That's one long sentence, and being a song lyric the sentence structure is upside down :) it's something like:

"Just so that the days when even your back shot felt like hope for tomorrow
would not disappear like illusions, I carved (the memory of your back shot) into my eyes; good bye"

I guess when he says "back shot" he is talking about looking at the lady walking away from him, and he means that he doesn't want that to disappear.