Do you know what medication he is on....if it is a Dopamine Agonist such as Requip, Ropinirole, Pramipexole....he may well be like this because he is suffering catastrophic side effects.
Lying, deceit, gambling, hypersexuality, aggression... are part of the obsessive compulsive behaviour that happens in a large number of patients on these drugs.
If so, it can be stopped and the drugs changed.
But you will need to tread carefully and try to find out what is at the root of this personality change.
There is a lot of help available here and elsewhere.
Perhaps the helpline as a starting point but it will be easier if you know what meds he is on.
Chin up and keep in touch.