“The dark never enters/ But it also never leaves” suggests that the problem does not come from the external, but it exist from within, which is why he cannot solve it.
Perhaps the speaker does not love his wife as much or the other way around.
“This spark that he gave you/ Is just an ember all but out” suggests that he cannot feel the sparks between them anymore; now the sparks become merely embers, and he is stuck in between, not knowing what to do, to endure the bitter marriage for his children or to let it go?
Here's the full interpretation of this song: https://en.lineday.co/snow-patrol-distant-bells-lyrics-meaning/
“The dark never enters/ But it also never leaves” suggests that the problem does not come from the external, but it exist from within, which is why he cannot solve it. Perhaps the speaker does not love his wife as much or the other way around. “This spark that he gave you/ Is just an ember all but out” suggests that he cannot feel the sparks between them anymore; now the sparks become merely embers, and he is stuck in between, not knowing what to do, to endure the bitter marriage for his children or to let it go? Here's the full interpretation of this song: https://en.lineday.co/snow-patrol-distant-bells-lyrics-meaning/