Launcelot’s past behavior leads to the conflict and the moral dilemma he faces in the siege of Benwick in the following way; The affair with Queen Guinevere forms the foundation of the conflict.
How the conflict escalated
The relationship fueled Gawain's vengeful rage, as Launcelot inadvertently killed his brothers years prior while defending Guinevere. This creates a simmering tension that erupts during the siege, that forced Launcelot to choose between defending his love for Guinevere and his loyalty to Arthur.
Lancelot is revered by many as a champion of justice and the embodiment of knightly ideals, but also suspected and resented by others for his perceived infidelity and potential threat to Arthur's rule.