Wickham was just 'a' favourite in Meryton. Certainly, Lydia's vision of 'tenderly flirting' with a number of officers at once does suggest she had no real partiality for him at that time. As an aside, I had to LOL at the idea of Lydia doing anything tenderly, let alone flirting!

However, in Brighton, Lydia was persuaded that she loved him alone. I wonder if all he wanted initially was a bed companion, but she insisted on marriage? Having convinced her that he planned to marry her, I am sure it would not take much effort for a man like Wickham to get her into bed before putting a ring on her finger.