Don't say NTs don't have this problem, because, funnily enough, a lot do. My mum is NT, and once her friend asked her to come with her to the cinema, and she didn't like the film what they were going to be watching, but she was panicking because she didn't want to say no. Also, my 28 year old cousin is NT, (and very confident and popular too), but she's letting her boyfriend boss her about and take over her life because she feels bad to say no to him, even though saying no to some things isn't nasty. And there are other NTs who I know who don't like saying no either.
But anyway, let's talk about Aspies here. Yes, this is more common in Aspies - I suffer from it too, and it makes life so hard. I've lost 3 friends in my past by putting my foot down, and I was surprised because I always thought being assertive was the only way to get on with people in life.
The first friend I lost was at school. I didn't want to stay on in sixth form with her, because the teachers had arranged a college course what would be good for me, and I wanted to, so I said yes. But my friend wanted to guilt me into staying on with her, and she knew I would give in - but I didn't, and on the very day before I started this new course, she didn't want to speak to me any more.
My second friend bullied me for being assertive. I had met this one in college, and we knew a boy who fancied me and my friend wanted me to go out with him, but I already had a boyfriend so I said no, and in the end a few horrible girls started bullying me - all because I had a boyfriend and so had to say no to this other boy (who I wouldn't have gone out with anyway).
And my third friend was the one I met at work, and he's much older than me. He wanted me to come round his, and every time I said, ''no I can't make it this week'', he always put back a nasty text - all because I said no. And I did see him a lot, but each time I had to say no, he got stroppy.
How the hell are you meant to be assertive and keep friends?!
I know the answer is probably ''you have to be assertive in the right ways'', but I was being assertive in the right ways. I had right reasons to say no, and I had no choice but to say no. And all these friends who have fallen out with me were NTs. I would have thought NTs would know better than to get the hump with me over nothing worth it.
See - NTs aren't always wonderful perfect socialisers what are experts at keeping friends. I've learnt a lot about NTs since I left school, and they aren't what we think. Maybe they know they can get the hump with whoever they like because they know they can always make other friends, so they tend not to cling to people, I don't know.
_________________
Female