How do you successfully manage a relationship with a sociopath if you?
Best option is to walk away - try to make a long term plan to get away/stay away from the person. If you can't, then assume that anything the sociopath says is a lie, unless there is independent corroboration. The more they get angry about you not trusting them, the likely they are to be lying. And anything they say related to money is almost certainly a lie.