Final answer:
The main conflict in the story involving Lancelot, Guinevere, and Sir Gawain is Lancelot's secret love affair with Guinevere. This conflict creates tension and leads to Sir Gawain's grudge towards Lancelot.
Step-by-step explanation:
The main conflict in the story involving Lancelot, Guinevere, and Sir Gawain is Lancelot's secret love affair with Guinevere, option 1. This conflict creates a tension between Lancelot and Sir Gawain, who holds a grudge towards Lancelot for betraying King Arthur and breaking the knightly code of conduct.
This conflict is a central theme in Arthurian legends and has been portrayed in various literary works.