Is there any way to stop nodes merging if you move them close together. It would be very helpful if there was.
There used to be a workaround but it doesn’t work anymore (I’m not sure which update caused the change)
In the past if you moved one node close to its neighbour, they would merge together. If you then pressed the undo button, you would undo the merge, but the node would reappear in the position that you had moved it to. This was a way to move nodes close together while preventing them from merging.
Now, however, if you press the undo button, the node reappears back in its original position. This makes it impossible to move nodes really close together.
Any help appreciated.
I use zoom in until you move without merge 
Most of the time zooming in works, but sometimes I find I need to line up a node with another part of my model, and it can only be done from a particular viewing angle and zoom; in this case it can sometimes be impossible to prevent unwanted merging.
Perhaps there could be a button next the snap/radius/twist buttons etc that would toggle merging on or off.
Alternatively, to prevent the need for an extra button, maybe the undo function could return to its previous behaviour: click undo once and it undoes the merge (but not the moving of the node), click it again and it undoes the move.
Another option will be to hide the back nodes and show only the ones in de current view.
Each point needs a lock option… it’s an annoying difficulty.
Just zoom
What do you mean by Nodes merging, could you show an example as to what I’m not understanding ? 
I mean the control points that you create along a path (the same as when you create a path(I think it’s called a curve technically) with trim/split/lathe tools etc. if the control points get too close they merge into each other. Usually you can zoom in closer to avoid this, though sometimes this is tricky.