Women are more likely than men to want a dating relationship to lead to a commited relationship. (Mathematically, that's why the average age at marriage is lower for women than it is for men.) Men are more likely than women to abandon a relationship because they "don't want to get serious."

This wanting sex without responsibility is, IMO, a sign of immaturity. The longer it goes on, the more a man gets in the habit of living as a perpetual adolescent.