My editor uses the game engine. That way it's more or less WYSIWYG, so what you're working on in the editor will pretty much be what to expect in-game. It's actually part of the main engine project but abstracted enough it could probably be a separate application and just reference the engine DLL. I use wxWidgets for the interface.
The actual 'game code' is not really referenced at all by the editor (it is in its own DLL), just the renderer is used. Everything is data driven so game entity definitions are loaded in from the script system which is actually separate from the game code. (part of the engine).
It does make things a bit more difficult, as normally you would have certain objects in different data structures (static objects vs. dynamic objects for example), and since any model can be moved around you need to be able quickly update these in the background. We also have a fairly complex shadow system so when lights are moved around part of their shadow maps need to be quickly recalculated as well (VSM shadows).
This is easy enough for small scenes but as levels get bigger and more complex you need to be able to do this super quickly so the editing experience is impacted by poor performance or things popping everywhere.
There are lots of other things like being able to hot-reload assets in the engine, which means a little bit of extra work on the resource managers, but this gives the added advantage that you can update a texture or model even when in the game without having to open up the editor.
The editor code isn't the prettiest (I don't think it ever is...) and is bit of work to get going but definitely worth it in the end. It's good being able to open the game up to test things out and having it look exactly as expected.
No one hates you, it's just that people would much rather have a demo to play with, or some code to go through, or a description of your technique (like you have done this time). These are all much more enjoyable and motivating than watching someone doing programming video tutorials (especially when they weren't planned out). Don't get discouraged because some tough guys on the internet gave you negative reputation ;)