He expresses indifference to everything that fails to give him a moment's amusement as he refers to his manservant's short marriage, "I don't know that I am much interested in your family life". Bills would likely pile in his flat in London on Half Moon Street, if he didn't tear them up. Responsibility isn't in his vocabulary, and he certainly doesn't place very much importance on being earnest. John (Jack) Worthing is Algy's best friend and is quite serious about everything that Algy takes for granted.
Although they do share a mutual fondness for a particular past time called "Bunburying" that involves the creation of a fictional double in the form of a brother or friend. The point of which to allow them to easily create excuses to travel as they like. Additionally Algy enjoys using his "Bunbury" character to avoid dinner with his aunt Lady Bracknell. He believes once a week is enough time to spend with relatives. While Jack utilizes his "Bunbury" character, ironically named Earnest, to see Algy's first cousin, Gwendolen Fairfax.
In the first act of the play, Algy was curious about an inscription in a cigarette case that Jack had left behind. The inscription read "From little Cecily, with her fondest love to her dear Uncle Jack". Up to this moment, Algy had only known Jack only by the name Ernest, but now Algy discovers Jack's own "Bunburying". Not seemingly fazed, as Algy seemed more interested in the specifics of the one named Cecily, he continued to question Jack about the case only to discover that Cecily is not Jack's niece, but his ward. Enticed by the thought of this young female ward of Jack's, Algy presses him by expressing his interest.
This results in Jack revealing that Cecily is "excessively pretty" and "only eighteen". Quite determined now, but resolving that he was "not going to be invited" by Jack, he decided to overhear Jack's conversation with Gwendolen. Fortunately for Algy, Jack reveals his country address to Gwendolen. Algy certainly had a scheme in his mind as he was writing down the address on his shirt cuff. Algy is quite a bored person. To avoid boring activities and to broaden his scope of entertainment, he created a fictitious character, Bunbury. As Bunbury, he can escape to the country side or just his aunt's dinners.
Algy also finds entertainment in being witty and appreciating life as an art form. He doesn't avoid scrapes as he "love scrapes". His scheme to see Cecily certainly turns into one, and many things change for him once he does finally meet Cecily. I think it is best summed up by Algy saying "I killed Bunbury this afternoon" when he had just told Jack that "Nothing will induce me to part with Bunbury". After meeting Cecily and falling madly in love with her, he's willing to give up his "freedom". Both he and Jack even resort to scheduling baptisms to correct their lies, and in turn both become earnest.
Algy always seemed quite amused with his own wit, even remarking on one occasion on his statement concerning women and their mothers, "It is perfectly phrased! ". He believed women to become their mothers while men don't become their fathers. He also shows his keen understanding of human behavior when remarking about the music selection for his aunt's dinner, "if one plays good music, people don't listen, and if one plays bad music people don't talk". Along with his wonderful taste in music, he's particularly fond of fashion.
He would "never have any appetite" without "a buttonhole first", and as much of a glutton he is, that's saying a lot. He also comments of the fashion of others or rather the lack thereof such as Jack and how he "has no taste in neckties at all". Another thing Algy knew, was that he loved Cecily and was willing to do anything to marry her. Algy may have fallen in love and forever lost his dear invalid friend, Bunbury, but his interest is fleeting. As well Cecily, for she even states she "hates waiting even five minutes for anybody". I believe it likely for their love to burn brightly and quickly.
A man that could fall in love with a woman in ten minutes and a woman that could love a man just for his name alone is not an ideal match. Although, their mutual whimsy could be that which makes them an ideal match. I would just hope Algy does as his said and forgets how after the proposal "the excitement is all over". Although, technically speaking, Algy never did propose to Cecily as they had been engaged nearly three months before they even met. It is widely believed that Algernon is a representation of Oscar Wilde himself, as both men are rather witty dandies that lead double lives.
While it can be argued whether Algy had truly changed, I'd like to think that he came to the realization "that Bunbury could not live". Algy had finally bumped into someone in that castle in the sky and was sure to provide him with plenty of entertainment as Cecily's imagination seemed to constantly create stories out of thin air. When she told him of their imaginary break up before they even met, Algy was "very much hurt indeed" and found Cecliy's reacceptance of the engagement to make her a "perfect angel".