The Scottish conflict flared up once again in 1306, when Robert the Bruce killed his rival John Comyn and declared himself the King of the Scots. Edward I mobilised a fresh army, but decided that this time his son would be formally in charge of the expedition. Prince Edward was made the Duke of Aquitaine and then, along with many other young men, he was knighted in a lavish ceremony at Westminster Abbey called the Feast of the Swans. Amid a huge feast in the neighbouring hall, reminiscent of Arthurian legends and crusading events, the assembly took a collective oath to defeat Bruce. It is unclear what role Prince Edward's forces played in the campaign that summer, which, under the orders of Edward I, saw a punitive, brutal retaliation against Bruce's faction in Scotland. Edward returned to England in September, where diplomatic negotiations to finalise a date for his wedding to Isabella continued.
During this time, Edward became close to Piers Gaveston, who was the son of one of the King's household knights whose lands lay adjacent to Gascony, and had himself joined Prince Edward's household in 1300, possibly on Edward I's instruction. The two got on well; Gaveston became a squire and was soon being referred to as a close companion of Edward, before being knighted by the King during the Feast of Swans in 1306. The King then exiled Gaveston to Gascony in 1307 for reasons that remain unclear. According to one chronicler, Edward had asked his father to allow him to give Gaveston the County of Ponthieu, and the King responded furiously, pulling his son's hair out in great handfuls, before exiling Gaveston. The official court records, however, show Gaveston being only temporarily exiled, supported by a comfortable stipend; no reason is given for the order, suggesting that it may have been an act aimed at punishing the prince in some way.
The possibility that Edward had a sexual relationship with Gaveston or his later favourites has been extensively discussed by historians, complicated by the paucity of surviving evidence to determine for certain the details of their relationships. Homosexuality was fiercely condemned by the Church in 14th-century England, equating it with heresy, but engaging in sex with another man did not necessarily define an individual's personal identity in the same way that it might in the 21st century. Edward and Gaveston both had sexual relationships with their wives, who bore them children; Edward also had an illegitimate son, and may also have had an affair with his niece, Eleanor de Clare.
The contemporary evidence supporting their homosexual relationship comes primarily from an anonymous chronicler in the 1320s who described how Edward "felt such love" for Gaveston that "he entered into a covenant of constancy, and bound himself with him before all other mortals with a bond of indissoluble love, firmly drawn up and fastened with a knot". The first specific suggestion that Edward engaged in sex with men was recorded in 1334, when Adam Orleton, the Bishop of Winchester, was accused of having stated in 1326 that Edward was a "sodomite", although Orleton defended himself by arguing that he had meant that Edward's advisor, Hugh Despenser the Younger, was a sodomite, rather than the late King. The Meaux Chronicle from the 1390s simply notes that Edward gave himself "too much to the vice of sodomy."
Alternatively, Edward and Gaveston may have simply been friends with a close working relationship. Contemporary chronicler comments are vaguely worded; Orleton's allegations were at least in part politically motivated, and are very similar to the highly politicised sodomy allegations made against Pope Boniface VIII and the Knights Templar in 1303 and 1308 respectively. Later accounts by chroniclers of Edward's activities may trace back to Orleton's original allegations, and were certainly adversely coloured by the events at the end of Edward's reign. Such historians as Michael Prestwich and Seymour Phillips have argued that the public nature of the English royal court would have made it unlikely that any homosexual affairs would have remained discreet; neither the contemporary Church, Edward's father nor his father-in-law appear to have made any adverse comments about Edward's sexual behaviour.
A more recent theory, proposed by the historian Pierre Chaplais, suggests that Edward and Gaveston entered into a bond of adoptive brotherhood. Compacts of adoptive brotherhood, in which the participants pledged to support each other in a form of "brotherhood-in-arms", were not unknown between close male friends in the Middle Ages. Many chroniclers described Edward and Gaveston's relationship as one of brotherhood, and one explicitly noted that Edward had taken Gaveston as his adopted brother. Chaplais argues that the pair may have made a formal compact in either 1300 or 1301, and that they would have seen any later promises they made to separate or to leave each other as having been made under duress, and therefore invalid. Such a compact, however, might not have excluded their relationship from having a sexual dimension as well.