Lyric discussion by zrated 

Cover art for Different Stars lyrics by Trespassers William

i think this song may be about a loved one who has died. not a lover, but maybe a parent; because of this:

"So you'd sing a lullaby to get me to sleep So it's no surprise my eyes are never heavy For I've not seen you in the flesh for so long That I'm not sure we would know each other at all"

like a parent might sing lullabys. this person has obviously been gone for a long time.

"Oh the weight it must be light wherever you are And I know you don't think twice wherever you are"

might indicate this person is in heaven, with no more cares or worries.

"So I will hum alone, too far from you All that I say now is nothing to you"

because they can't hear her where they are and earthly concerns are no longer of consequence.

"We will lie under different stars I am where I am, and you're where you are You're where you are"

it hints at a different circumstance of existence. as in the two cannot be together for physical reasons, like being on two different existential planes, rather than emotional reasons.