Is Bipolar Real or A Thought?

My husband and I raised three beautiful children. All left the nest and are pursuing their higher education and while two are very successful in every area of their lives, for our youngest child, we are called to ‘save him’ every few months from another problem.
Once he was found smoking pot, then he was found selling it, and both incidents cost us lawyers and stress while we were trying to prevent him from going to jail.
After the last incident, we took him to a therapist and he was diagnosed as bipolar and was given drugs to treat it.
He says he feels amazing for the first time in his life, alas, on Thanksgiving dinner he revealed to us all that he has been fooling Uber drivers as he found a ‘hole in the system’ and so he has been using them for six months and not been paying.
We expressed our concern with him and said this is nothing to be impressed about and that he could get sued any day if they found out. Everyone at the table, old and young, told him this is a bad idea. He said he is not to blame, that it’s him being bipolar.

Since he is above 18 and doesn’t live at home anymore, there is only so much we can do to control his behavior, but we are concerned that he is using the bipolar diagnosis to justify his behavior.
Is there a place to even introduce the Model and thought work to him or are bipolar people don’t have the same thinking capacity as we all do?