How did David lose all his things and money ?

I don't think that David ever did have a lot of money and many things. The striving for social status can be seen through David's and Dora's courtship and marriage. David's first thought after hearing of Miss Betsey's financial downfall is shame at being poor, and Dora cries at the thought of David being poor and of having to do her own housework. David is constantly striving to make money so that he can live and provide Dora with a life of wealth. Little Em'ly also expresses unhappiness at her low social status and longs to be a "lady," which is why she runs off with Steerforth in the first place.