The speaker is ending a relationship, but not because the love has run out. That's the twist in the first lines: leaving usually means love has faded, and here it hasn't. What has faded is the speaker's love for themselves. The longer they stay, the smaller they feel, and walking away becomes a way of protecting what's left.
The short, plain lines make the confession feel quiet and tired rather than dramatic. Then the poem shifts into one long closing sentence. The speaker admits the idea once "sounded crazy and illogical," as if they used to think you should never leave someone you still love. Only after living through something painful, which they call "hell on earth," did it make sense. The mood is sad but steady. There's grief in it, yet also a hard-won clarity, and the title, "At last," suggests relief at finally choosing themselves.