If you had a written agreement governing the partnership, then the terms of that agreement, if they address dissolutions of the partnership, would apply. Without a written agreement, there is substantial likelihood of legal trouble or conflict down the road, if your ex-partner seeks it:1) Since even without a written agreement, he presumably worked with at least an oral agreement and reasonable expectation of compensation for his contribution, he could, depending on how much of his work you use, potentially sue you for a share of any profits.2) He could take the basic idea and run with it on his own, since an idea (not the creative work, like writing or drawing, embodying it, but just  the idea itself) is not protectible unless there was a confidentiality or non-disclosure agreement of some sort.As a very rough rule of thumb, you could proceed on your idea but should not use any work he did; and you need to be prepared that he may be developing this in parallel (but he likely couldn't use your work without paying you). However, all situations are different, and their specific facts affect your legal rights. You are advised to consult with an attorney in detail about your situation and goals.