The whole poem is based on an extended metaphor comparing a passionate phone exchange between lovers to a showdown between gunslingers in the Wild West.
The poem's title introduces this metaphor. "Quickdraw" refers to a competition between two people wielding guns: whoever unholsters and fires their gun and hits their target the fastest wins. The rest of the poem then builds on this metaphor, treating the speaker and their lover as the gunslingers, their phones as the guns, and their messages/voices as the bullets.
Through this extended metaphor, the poem conveys the intensity, passion, and danger of the relationship between these people. Both have the power to seriously hurt the other. Indeed, in the first stanza, the speaker says that their lover draws first; the "pellet" (or small bullet) of their voice makes the speaker "groan" in pain, pleasure, or both. The speaker has been "wounded," the implication being that the lover has said something devastating.
The speaker fires off their own words in response, comparing their "tongue" to the "trigger" of a gun. Yet their words are "wide of the mark"—they miss their target, suggesting that the speaker isn't as good at this game as their lover is. This, in turn, might suggest the lover has more power in the relationship than the speaker.
Indeed, the speaker says that, after they miss, their lover "blast[s]" them "through the heart." This could again be interpreted as a description of either pleasure or pain, but it again illustrates just how powerful, and dangerous, passion romantic passion can feel.
The speaker says that this melodrama, this mix of intense pleasure and equally intense pain, "is love." By equating "love" with the cliché of the old Wild West—"high noon, calamity, hard liquor"—the speaker seems to acknowledge the way love itself is riddled with clichés: falling in love can feel cheesy, wild, serious, ridiculous, and intense all at once.
What follows is a scene seemingly straight out of an old Western: the speaker holds their cellphone up in the air where the "sheriff" can see it, apparently surrendering their "weapon." But really they have a second phone "concealed" in their "boot." In other words, the speaker is playing dirty: they want to win this game! But their lover once again gets the upper hand: they "text" both phones "at once" and the speaker "reels" and "fumble[s]" after their phone, "read[ing] the silver bullets" their lover has sent them.
A silver bullet refers to something that instantly, and seemingly magically, solves a problem; the implication is that whatever the speaker's lover has just said has broken past all the speaker's defenses and fixed whatever tension has been bubbling between them. Instead of firing back, they appear to give in. The poem ends with the speaker being metaphorically riddled by bullet-like kisses, suggesting that their lover has won the game—the speaker is overcome with pleasure.