In Pride and Prejudice, how do we know that Lydia and Wickham's marriage is not working out?

I don't think there is a direct statement that this
marriage is failing, but when we recollect the moral and intellectual character of Lydia
and Wickham, we don't have much to hope for.  Lydia is silly, flirtatious and boy
crazy.  Her "eloping" with Wickham was not to get married, even though she may have
foolishly thought so.  It is only for a substantial financial settlement from Darcy that
Wickham agrees to make the situation right and save Lydia's reputation.  Darcy not only
gives Wickham money, he also purchases Wickham a commission in the army to provide for
their future.  We know that Wickham always intended to make his fortune through
marriage.  He tried to pull the same tactic with Georgianna!  He lost interest in
Elizabeth, and shifted his