contract between brothers

[Gabriel DeSantis]

My brother and I decided to buy a house together 3 years ago. Our plan was to keep it as our primary residence for 5-10 years. We opened a joint account to pay for all our house expenses. Each month we contributed 50/50 and accounted for mortgage, insurance, utilities, and maintenance. The house has been great and did not need any major maintenance. 

Now he is getting married in September and buying another house with his wife. I was forced to refinance and buy him out early. He is currently renting from me until his closing at the end of the month. He believes that our house account should be split. 

My idea was the house account is our insurance policy in case something went wrong and that money should stay with the house. How should I handle this.