Y are u making a big deal out of this? You moved back to try and fix things and your already fighting over nothing. Just give him the reciept and be done with it. Its not a big deal. I got a reciept for my deposit on our house. We both signed it. If you want this relationship to work, then you gotta let the past in the past, let go of your resentment and give him the chance to prove he can man up without reminding him of all his failures
also stop mothering him. Just STOP. Let him pay you monthly, let him get his own ass outa bed in the morn, let him take responsibility for HIS study,exams, pay etc and if nothing improves in the next few months WALK AWAY
I think you have taken on the responsible role and put yourself in charge and in control of finances. Y dont you change that? Go to your landlord and set up two separate accounts for rent. Let him sink or swim as WU said. Set up a houseshare agreement or something where your only responsible for you and top worrying. Let him buget himself-he may learn better responsibility that way