I have been 'friends' with someone for around a year or so. Initially we spent quite a bit of time together and then it tailed off a bit, probably as you'd expect. We have a few other mutual friends, although they are more her friends than mine really.
I felt a little uncomfortable with the friendship as she quite actively slagged people we both know off, who she appears to be friends with. Also, she confided in an affair or fling to me and I felt dreadful knowing this as I have met her DH a few times. However, she had a dreadful and abusive childhood and ended up in care etc and still seems to suffer the effects of this so I put it down to that really.
However, there have been a number of things we had arranged to go to together and she'd often let me down at the last minute. The last thing like this I text her on the morning of the thing to confirm she was going as I had got up late etc and probably wouldn't bother if she wasn't going afterall, which I told her. She said she wasn't going, but then later I found out she had gone after all. There have also been quite afew nights out with the mutual friends to which I haven't been invited.
Then I found out that she had arranged a party on Saturday night and hadn't invited me. I text her and asked if I had upset her in some way as I hadn't been invited and she said she just hadn't seen me (she has my phone numbers etc) but I was welcome and of course I hadn't upset her. So, I went along and when I arrived I rang the bell a few times, one of the DC finally let me in and I went into the living room to say Hello and she ignored me. There was loud music etc, so I assumed she hadn't heard me and went and got a drink. Later on she seemed fine, chatty etc. However, today one of the mutual friends asked what had happened to make A ignore me at the party as when I had rung the bell she had heard and said, oh, that will be jolly' but then not got the door and ignored me when I came in. 
There are occasions where A does ask if I am going to a toddler morning or something, so I find it all a bit confusing and feel I should just distance myself, but I don't have many friends really. I just don't understand what is going on and I feel she doesn't really want to be friends with me?