How long have you been in US

I am sorry for what happened to you.
I would say that you kept” Chinese style" when you loaned money to him. As american he won't feel unconformable if you let him sign any loan document.

One thing you may also need to pay attention. He may consider that he earned that amount money because he helped you to win the case you mentioned. He can say you paid him as commission and you have to be ready for it when you sue

good luck