Consider his actions as good examples of his character (we often judge people by what they do as much as by what they say).
At the start of Book 6, in chapter 1, Lancelot is not happy sitting idly by, but instead he seeks a life filled with action and adventure:
"Thus Sir Launcelot rested him long with play and game. And then he thought himself to prove himself in strange adventures, then he bade his nephew, Sir Lionel, for to make him ready; for we two will seek adventures."
In chapter 3, Lancelot proves that he is loyal to his Queen, respectful of her as a woman, and is not the sort of man to have casual relations with a woman:
"...I will none of you, for ye be false enchantresses, and as for my lady, Dame Guenever, were I at my liberty as I was, I would prove it on you or on yours, that she is the truest lady unto her lord living."
In chapters 7-9, we learn of Lancelot's bravery as he seeks out Sir Tarquine in order to save his fellow knights who have been captured and to end the reign of terror Tarquine has established.
Other character traits continue to be revealed and reinforced based upon his actions as his tale continues. I used the electronic text from the University of Virginia Library (see the link) to respond to your question. Adaptations may vary.