It's weird, I have a few single childless female friends in their forties and they genuinely think that "mothers" look down on them for not having children. I've read stupid articles in the Guardian about this phenomenon and never once witnessed it.
Having said that, it's not pity, and it's not 'looking down on', but out of my friends who have been single for years, there is not one I would consider dependable. They live their own lives which are full and interesting and free - that's great. But in their cases there's a lack of understanding of the mechanics of keeping a relationship going, having children who need you, having (zzz) domestic commitments etc. It doesn't half get in the way.
Examples: you go on holiday with friends, and the two single women announce they will not be cooking because they can't. So...we're going to look after you? Really? Pitch in!!
My single friend likes to come round and chat, but I need to cook a family meal, supervise homework...she thinks I am making a comment on the emptiness of her home life when I tell her I'm going to have to get on.
And the broken arrangements: "I just feel a bit like staying in today, so I won't be coming' - thanks, I had to negotiate those two hours off at the weekend with my family, cheers for that.
So basically a bit of a lack of understanding.