Needs: A lot of the time it simply boils down to lack of time. I have different "types" of people who I like to socialise with, in all kinds of different ways: people who I met through work, SILs, mums I've met through the kids, my mum and sis, oh - and DH of course! Ideally, I would LOVE to go out for a drink with the other mums of an evening or at the weekend, but there are only so many free evenings and weekends that i have because a) DH often works very late so I can hardly ever go out mid-week, and b) I work on a Sunday.
This means that we only have Saturday to do family things together or even just tidy the garden or get on with other stuff like that. So that is really precious time. I'm not saying that I don't EVER meet up with friends on a Saturday without the kids or something, because I do - it's just not that regularly. Luckily my childless friends understand and continue to invite me to things in the knowledge that I would possibly have to turn them down cos I've got to take DS to a birthday party of something. Point is, they STILL continue to invite me despite me having to "knock them back" fairly often. To me, that is a sign of a true friendship and I'm very lucky to have them and appreciate the way they are.
On the other hand, when I DO have a free evening,I am very wary of inviting child-free friends to go out for a drink in case it looks like I'm just "using them". Silly really as I know they really don't see it like that.
I've just started becoming acquaintances/forming tentative friendships with other mums now DS has started school now, too. We've tended to meet up after school with the kids at someone's house so far. Whilst it would be nice to meet up with them sans enfants to go for a drink, I know how busy people's lives are, so so far this hasn't happened. Money is also a consideration for us too now - I could have all the free time in the world but still have no money to afford numerous nights out with various friends every week.
I think I'm trying to say (amidst all the waffle ) that it's sometimes quite important not to jump to conclusions about why someone turns you down for meeting up without the kids. It doesn't have to mean anything except that they are short of time, money or babysitters. That's all, so I think you ARE being a little bit paranoid, yes!
Oh yes, one last thing. Someone mentioned how hurt they were when their friend moved away to a new area and didn't return their calls. I got quite friendly with a woman who lives down the road when our kids were at nursery. Now our kids have started separate schools, and neither of us has phoned the other, despite us getting on quite well. I am presuming it's simply down to lack of time, rather than the fact that our friendship wasn't worth continuing. Perhaps, after reading this thread I'll get off my butt and give her a call and arrange a little get-together.