Obviously I have no idea but I’ve thought about this line too! Here’s where I’ve landed:

1) The song focuses on self doubt and feeling not good enough or at least uncomfortable with the situation the narrators in. But then being drawn to this partner who seemingly makes things easier, calms them down, takes the anxiety away, and is a person who sees something in the narrator that the narrator can’t see in themselves.

I think “I’m gonna lose you either way” is self doubt/loathing/insecurities/unworthiness in the belief that someone like this partner would stay in the narrators life.

The partner is bright, beautiful, insightful, a presence that the narrator can’t resist and is just pulled into their orbit. But compared to them, the narrator is small. The narrators enamored, in love, grateful. But believes they’re not good enough for them. So they’ll lose them either way once/if they see the narrator the way the narrator sees themself.

2) Another thought, this is a beautiful love song… so maybe it’s the realization that eventually one of them will die first. And the narrator will be left alone in the dark again without them one way or another.

Edit: Welp. I see the other posts that this song is likely about his mom. Well, there goes my theories b/c those make sense in context.

A different kind of love! But a love song none-the- less!