I was thinking about friendships in general. Some people are really good at sparking up friendships, some less so. Some, whilst good at making friends, are less so about keeping them (I think I'm channeling Colin Firth as Darcy there 
).
Some simply won't extend themselves for anybody who they deem "not worth their time", for any variety of reasons. I honestly doubt your status as a single parent weighs heavily on most minds. Some might be looking at your bag, think "tchah! not Mulberry, darling..." Seriously, it can be that shallow (and who'd want that kind of person for a friend anyway?!?).
OTOH, some of what you might be interpreting as snubs might not be. Sometimes people are so wrapped up in their own lives in general, or even just thinking about things on a day, they didn't even realise they've just snubbed someone (not necc the case at the pageant t'other day, but possible).
I speak as a [fellow?] depressive: 99 times out of 100, it ain't about me. And the sooner you - ahem, for want of better word - unclench and stop taking responsibility for other people's social skills or headspace, the sooner you'll taste that delicious freedom to just Be Yourself.
And yourself is lovely to behold, so roll on Being!