Lizzy's view of Wickham's motives is to be found in Volume lll Ch IX:

"She had scarcely needed her present observation to be satisfied, from the reason of things that their elopement had been brought on by the strength of (Lydia's) love, rather than by his; and she would have wondered why, without violently caring for her, he chose to elope with her at all, had she not felt certain that his flight was rendered necessary by distress of circumstances; and if that were the case, he was not the young man to resist an opportunity of having a companion."