How does Wilde explore the subject of marriage and pleasure in this scene from The Importance of Being Earnest, at the beginning of Act 1?
ALGERNON: "My dear fellow, the way you flirt with Gwendolen is perfectly disgraceful. It is almost as bad as the way Gwendolen flirts with you",
ALGERNON: "Then your wife will. You don't seem to realise, that in married life three is company and two is none".
As a true representative of the aesthetic movement, Wilde holds true to the movement's views on morality, artificiality, and superficiality.
The movement's motto of "L'Art pour L'Art", or "Art for Art's sake" entails that life should imitate art; hence, life should be lived in whichever way we wish to portray ourselves, and our masks, to the world.
As Wilde's mouthpiece, Algernon follows the tenets of aestheticism by presenting himself to the world as a hedonist (pleasure-seeker), as a bachelor, and as someone who would much rather explore life on the surface than in-depth. He does this shamelessly precisely because he strongly adheres to the idea that his life should always be enjoyed and overindulged.
Marriage, in the true sense, is a very in-depth compromise of loyalty and love. These are all concepts that go directly against the beliefs of a sybarite like Algy and, for that reason, he despises the idea.
In his world, romance is better than love because it is more exciting and requires no compromise. Marriage, in his view, kills romance because all you have is the same two people engaging in the same daily dynamics over and over again. That, by no means can be any fun; it turns romance dull, boring, and sour. You need a third person to kill the routine.
Hence, Algy's conclusion is that marriage cannot equate pleasure, and vice versa. If Jack gets too involved with Gwendolen, it would mean the end of all the fun vice that Algy and Jack enjoy together in London; in Algy's view, for Jack and Algy to remain happy, they should continue to merely scrape the surface of the "serious" things in life and continue to make their own lives quite trivial.