I kind of agree with the others here but maybe I'm not so pessimistic. He did pay you back the first time and has again. That's a big plus that usually does not happen. But he's really got to grow up an stop using you as his bank. If his business needs short term cash flow financing (and most businesses do at times) then he would be far better off going to a real bank, learning to present them a solid business plan, and getting financing that way. Quite frankly, if he wants to borrow money from you again you need to make him do that for you. Make sure he has a solid plan with specific dates for repayment, and collateral. I suspect that will tick him off though.
To save your relationship you probably want to start locking that money away in investments like mutual funds or CDs so that the cash is not enticing him. Just tell him that you (singular) want save for your (plural) future just like he is building a business for your future. If he argues with that then you should be worried.