Dacey's poem sketches a familiar pattern: the first person you fall for tends to be the first person who hurts you. The speaker lists the steps in a short, almost matter-of-fact chain. First comes the "first try" at love, then the "first lie," then the "first goodbye," and finally the broken heart. Each stage follows the last as if it were inevitable.
The speaker sounds resigned, maybe a little bitter, but not dramatic. The short lines and the repeated word "first" make the whole thing feel like a rule everyone learns the hard way. The phrase "don't forget the broken heart" has a dry, knowing tone, as if the speaker is reminding us of something we'd rather skip over.
The poem ends on a comma rather than a full stop, which leaves the thought hanging. That could suggest the pain isn't fully finished, or that more experiences will follow. The mood is wistful and rueful, the voice of someone looking back on a first love with a wry shrug.