Purple what does WN stand for sorry? I'm going to guess wanker narc, or similar. Am I close?
I hope you've not had multiple narcs to deal with. 
Lilac DS is only 3.5 but regularly says that he doesn't want to see his daddy, or that he doesn't want to go on his own.
Ex is really unkind in the way he speak to DS so I'm not surprised DS isn't keen on him! For example, at the weekend DS was messing around and sticking his tongue out, and ex snapped at him 'you're not a dog, are you?!' In a really aggressive tone.
I felt like replying with: "No, but you're a c*nt aren't you." And walking off wth DS but I didn't. Wish I had now after tonight. 
I do think it is more stress than it's worth, yes. I'm not expecting it to last long. He has only been back in contact since the last weekend in June and he already can't be bothered. He has dipped in and out in the past and when DS was smaller, it didn't cause as many issues. If he decides to bugger off again then it will be for the last time because I won't be putting DS through it again.
His excuse for his behaviour and constant cancelling of contact/expecting me to rearrange with hardly any notice is that I ONCE asked him if he could see him on a Saturday instead of a Sunday as we'd been invited to a christening. I asked if it was ok, where as he demands things and tells me what is happening.
Sorry.
I'm really wound up if you couldn't tell.