I mean, I do want to give back to the community but I really don't want to give code snippets that work out of the box to my formers competitors you see ?
Well, is it even a valid concern ?
Basically you are pissed at them because they won in the market space. That's a perfectly normal and acceptable perspective to take. The only problem here is that you have only seen the one set of users that would get your code: your competitors. If you GPL'd your code they wouldn't be able to legally use it any way; in most cases.
The other set of users would be the [potential] contributors. They would take your code, improve it and bring it back into the repository. Eventually that open source repository would be worth more than anything your competitors would be able to put together.
Basically, from where I am sitting, open sourcing your code is the best path to getting revenge (face it, that's what you are after).
Why are you worrying about competitors? If you're at a point where you have stopped working on it and are considering open sourcing it, it should make you happy that your competitors are using your code haha.
Unless you have any benefits to gain from not open sourcing it, then open source it. If you do, contributions from the open source community might just enlighten you and you'd be a more educated person in terms of how to execute ideas efficiently.
In a business sense, open sourcing it can allow you to gain recognition, visibility and goodwill.
In a personal sense it could offer fulfilment, and in a moral sense, like you say, you are giving back to the community.
However, be prepared to spend some time in cleaning commenting and documenting if you really want it to be of use to others..