Lyric discussion by Floyddead 

It didn't actually say any where in the song that she left him for soeone else. Where did you hear that??

Perhaps he was woundering if he should or should not say goodbye. Maybe he felt hard done by.

"If I never lived without you, Now you know I'd die." This line suggests that she gave him such strength that he wouldn't be able to live without her. But in reality, I'm sure he'd have got on just fine, unless of course he's suggesting that he was thinking of committing suicide, & she convinced him not to.

"If I never said I loved you, Now you know I'd try" Perhaps he never found the courage to say he loved her, & regrets it, and perhaps that's why he lost her.

She now knows he'd try, possibly because he got drunk some night & revealed the way he felt for her, while strumbling and reaching out in desperation, but to late.

My interpretation may sound weird, but that's what I picked up from it.

@Floyddead For "If I never said I loved you, Now you know I'd try", that could go back to what you said before about him trying to kill himself, where had he never said he loved her, she wouldn't be with him, and he would have tried to kill himself.

An error occured.