There’s a bit of a paradox in your question because you talk about his moral oblgations whilst asking, effectively, whether you should have made a contract of legal obligations in advance.
I think it unlikely you are going to sue your colleague so what you are really looking for is in endorsement of your view that he has a moral obligation to put you right. Which he does, obviously. One cannot just borrow someone else’s stuff, return it in a complete state and then wander off whistling to themselves as if nothing had happened. We don’t live in a World where a conversation about his duty to look after your stuff needed to have been had in advance. It goes without saying.