There are some people who get married and are soon very bored or feeling too confined with marriage.
Male or Female, gay or straight, they would be better off keeping their own place rather than moving in. They would be better off making their own money or spending the money they're supported with the way want to, without always having to confer and agree with a spouse. They need some separate vacations, separate friends, separate interests. Maybe they are a bit too independent for a traditional marital lifestyle.
Maybe their relationship would be better if they were never married.