The speaker is afraid of being left, and the whole poem is built around that fear. It opens with a reminder of a promise, "You promised not to leave," but what follows isn't a calm argument. The speaker lists all the ways the other person would be better off without them: no insecurities to manage, no worry about reputation, no pressure to keep someone happy. It sounds generous, but it reads more like self-punishment. The speaker seems to believe they are "a lot of work" and "not enough," and they say so as if it were simply fact.
The mood is quiet, anxious, and sad. The short, flat lines give the feeling of someone trying to stay calm while falling apart. "I'll be crushed" is stated plainly, then quickly buried under reassurance for the other person. The ending, "It'll all be over," is ambiguous. It could mean the relationship, or it could hint at something darker, and the poem leaves that uncomfortably open.