、。
Heads, I win; tails, you win.
Literal
Front [subject-が] came-out [conditional-たら] my win, back [subject-が] came-out [conditional-たら] your win.
表が出たら僕の勝ち、裏が出たら君の勝ち — parallel conditional structure using たら. 出る means 'to come out/appear' for coin faces. 僕 and 君 mark it as casual male speech. The symmetry makes it easy to parse.