No, he is not interested in "the opinion of neutral parties." He couldn't care less about any opinion from anyone. He is a compulsive spender. You are in pretty much the same situation as a person in love with, and living with, a compulsive gambler or an alcoholic. He is going to avoid paying you back what you loaned him. Plus, he'll be looking to borrow more money from you within 2 years time. Just say "No."

Insulate yourself from him financially as much as you can. No joint bank accounts. No shared credit card accounts. Understand that his behavior is compulsive. He may be incapable of changing it. You are the one who needs to change her behavior. That is all you have any control over.

If you take the approach I suggest, expect that he will be angered and resentful. Do not try to reason him out of those feelings. You'll get nowhere. Do not engage in argument with him over money matters. Don't try to defend your decisions to him. He'll reject every defence and rationale you offer. In your heart, you know that he has exploited you financially, and that what he's done is dishonorable and shameful. You, however, have started early on to enable him. Then you doubled down on the enabling. Then you tripled down. Stop it. You are addicted to "helping him." It's like you've been baking sugary cakes for a severe, insulin dependent diabetic. You do it because you're afraid he won't love you, if you don't. That may be true . . . in which case he mainly values you as a meal ticket. No one needs that kind of love.

I'm glad his legal practice has been lucrative lately. That won't last. This man is so profoundly immature and irresponsible and bereft of integrity that nothing he undertakes will succeed for long. His spending will always outstrip his earnings. He'll get bored with the BMW and decide he needs a Lamborgini. He is very much repeating the example his father set - inability to commit to living responsibly. He may lack the character to ever change.

You don't need a 3rd party to referee your discussions with him about financial matters. You need to stop having those discussions. You're hoping he'll give you permission to be fair to yourself. He never, ever will. You don't need your therapist to tell you what's fair, or to come up with clever ways of describing how he is "cheating" on you. You have cheated you by giving him ridiculous amounts of financial support. Stop doing that. It's your money - hold on to it. Or - alternatively - recognize that he wants a "sugar mama," and that you are willing to be that, in order to keep him happily hanging around you.