Few words carry a lot of weight here. The speaker is addressing someone they used to be with, and the poem opens with a hard admission: that person went on living without them, and things didn't improve. It's not clear whether the speaker is glad or sorry about that, and that uncertainty is part of what makes the line sting. It sounds like a quiet observation, but it also sounds like guilt.
The apology, "i'm sorry," sits alone on its own line, as if the speaker can't manage anything more around it. Then comes the real confession: they wanted the person back, but were afraid things would simply repeat. The poem never says what "the same" means, so we're left to imagine the pattern they dreaded.
The mood is hushed, regretful, and stuck. The title, "separate," fits: the speaker is apart from this person and from their own choices, caught between longing and fear.