first of all WTF? 50 lakh cash??
ask him to transfer some property worth your loan amount in your name until he pays back the loan, forget the friendship, he’ll try to manipulate by saying “Don’t you trust me” n all that, you’ll have to manipulate him back by saying I dont have much left, and that you;ll need the money soon for a house construction, or your parents illness, or your family etc
either this
or ask for a post dated cheque(you can date it upto 1 year from the previous due date), in his name, a single cheque that is the same amount as your agreed amount, give him another year to pay back, if he doesn’t, the cheque will bounce and then you can pursue this legally.
keep all the chats screenshots, and if you decide to pursue this legally, then get ready to show where you got 50 lakh in cash from and the taxes that you didn;t pay on it.