My love for you is not a creature of chance or fortune but something built far from accident, standing immobile against time's fashion and change.
The speaker contrasts his love with 'the child of state'—a bastard of fortune that could be unfathered. His love is instead 'builded far from accident,' suggesting an architectural permanence. It 'suffers not in smiling pomp, nor falls / Under the blow of thralled discontent.' Love is immune to the fashion cycles that Time orchestrates. The metaphor shifts from accident to architecture: love is a built thing, stable and founded.
Crucially, the love 'stands hugely politic' while avoiding the 'policy' that earlier sonnets associated with corruption and calculation. It is politically astute (politic) without being politically manipulative (policy). It 'nor grows with heat, nor drowns with showers'—it's invulnerable to emotional fluctuation and circumstance. The couplet calls as 'witness' the 'fools of time, / Which die for goodness, who have lived for crime'—those whose values shift with fortune are the real fools.
Your relationship didn't happen because of timing or luck. It's not a creature of Instagram algorithms and matched interests. It's something architecturally different—it would survive any circumstance, any economy, any trend.