What did Mr.Darcy determine were Wickham's intentions in running away with Lydia?

Wickham owed a large sum of money and was basically going AWAL from his regiment. He knew Lydia had a major crush on him and wanted to take her along for "companionship". I don't think he intended on marrying her. He would have dumped her at his first chance thereby ruining Lydia's and the Bennet's reputation forever. It wasn't until Darcy basically bribed him to marry Lydia that he changed his mind.