So, this is probably an issue most people have had to deal with at some point. Maybe you guys can help me have some better perspective on this.

I've lost friends before - either we've grown apart, or we've fought, or I was a shitty friend (during the time when I was with my abusive ex). But I don't think, in my entire life, I've ever really tried to be friends with someone only to have them completely seem uninterested in friendship. Except this one time.

She's a friend of one of my closest friends. We were in our mutual friend's wedding together. We have a lot in common. I find her interesting. Sometimes she's nice to me - she's invited me to parties, she'll talk to me. In the past it's seemed like all the signs were there that she wanted to be friends. But when I started actually trying to be a real friend to her, it seemed to fall through. She was polite, and would hang out with me when I initiated times to hang out, but seemed uninterested in getting closer. Sometimes our mutual friend would tell me things about her, things that weren't immediately a secret (and I'm a really not private person, so unless you explicitly tell me or unless it's like glaringly obvious, I'll probably assume it's not a secret). Then I would mention them to her and hear months later through the grapevine that she was upset that I knew.

Obviously she just doesn't want to be friends. Which should be fine. Not everyone has to be my friend. So why does it make me feel so shitty? And how do I convince myself not to feel a little pang of rejection every time anyone talks about her to me? Logically it shouldn't even matter. But it does for some reason. And most of all I just want to know the reason she doesn't want to be friends with me.