BERKSHIRE, UK—An 18-year-old schoolboy has criticized the culture of casual sex, saying it brings unhappiness rather than satisfaction.

Phin Lyman told his school magazine why he is abstaining from sex and described his concern over the level of peer pressure on young people regarding casual sex.

He rejects the idea that he is missing out: “I really believe I am not. The people sleeping around are the unhappy ones.”

Lyman studies at Wellington College, a co-educational day and boarding school in the United Kingdom’s Berkshire.

He notes, “I would say 90 percent of people are drunk when they los...