How soon might he want it again?
And, moreover, he could not repay the money without explaining to her how he had gotten it.

It would be preferable to say nothing about his money.

As he let himself into the house and went up to his room he resolved that he would not say anything about it.
On that morning he was at the station at nine, and hunted down in Buckinghamshire, riding two of Dolly Longestaffe's horses for the use of which he paid Dolly Longestaffe's 'fellow' thirty shilling..