When is a "real" lie?

I have a bf who has a history of not fully telling the truth about his money issues. Since he wants to live with me and possibly, marry, his truthfulness of this issue is critical. We've been together several years and he knows that until I'm satisfied he is not playing games with reality, I can't move forward with him. He promised me he is a "changed man" and is totally responsible with his finances.
He had been using is elderly mother's credit card for certain items last year when he was unemployed and told me she knew about it. She is essentially destitute and ready to go on Medicaid and has Alzheimer's. The card in question is almost at its max and he pays it with her funds (I believe) nominal amounts just to keep the card open for emergencies.

He has been re-employed for several months ago and apparently paying his own bills but I learned a magazine subscription he must have ordered last Fall when he was unemployed and used her card, was renewed almost 2 months ago and charged to his mother's account. I know he sees her bills and makes the modest payments so I assume he saw the charge on the May statement.
My question is: I am not aware of whose money the nominal payments on the account came from, but have good reason to believe it is his mother's money; isn't this a lie? Even if it he used his some of his money to pay his mother's card, is it still dishonest?
He has told me in the past he has no intent to pay off her card since once she passes, there will be no money to pay it.