I'll try to keep the backstory short.

About 2 years ago, my friend and I thought of an idea. That idea isn't exactly a product, it's more like the brains behind any product we wish to pursue. It's blocks of code. A year later we decided to apply this said "brains" into an actual product. But somewhere along the way, we didn't see eye to eye on where the product was going and as the person who was dedicating most (actually, all) of the time into the development of the product while my partner did nothing, I felt I wasn't heard. So I came to him with a different proposition: something on the side we can work on along the similar field of what we're doing which could yield fruit. In a fit of rage, he said: 'Either you're working on this with me or you're going there.' Now this was my pet project, I dedicated countless of sleepless nights developing. The "brains" which I mentioned earlier came from me. I have the code etched into my mind to the last semicolon. All 748 lines of it. I said: "Sure you can keep this product, I don't care anymore. Good luck." and left.

Lesson learned, choose your partner wisely. Now onto my question. It's been a few months now, and since I've been gone, There doesn't seem to be any progress on the project in terms of development from my ex-partner. Except he found a new partner and updated the information page about the product with some new images of probably a just an adobe design mockup. I have decided to take a new approach to the product we were originally creating before it turned into some strange concoction of Facebook and snapchat. The problem is, I want to use the brains of the application. I coded it 2 years ago, and now I've refined and improved it on my own, leaving my ex-partner with a piece of code made years earlier. I'm not releasing the same product they are, could it cause legal conflict? It'll be fairly obvious I am using the idea I formed with my ex-partner when I launch my product, but none of the code is the same anymore.

P.S. I am 100% sure I can beat them to market.