My (28F) colleague (30F) didn't invite me to her wedding, and it's completely unravelled our friendship

One of my work colleagues is a lifelong friend of mine. We lived on the same street growing up, went to the same school and when I needed a job after graduating university, she made me aware of an opening at the company she worked at. I applied, got the job, and it's been quite a few years since and we still work together.
It's a pretty small company, and quite male-dominated, so after we started working together we became really close. We take all our lunches together, we regularly stop by each other's desks for a chat, and we quickly became known round the office as inseparable.
A year ago she got engaged to her long term partner, and I was ecstatic for her. She had a really tough time a couple of years ago (two family deaths close together) and I did everything I could to be a good friend to her while she was in the worst stages of grieving. She cried with me daily for weeks and I made sure she knew I was always available to listen. I also took about a third of her workload off her voluntarily, so she could take days off when she needed to without stressing about her work building up. So now that life has gotten better for her and she's always smiling and excited, it's really nice to see.
Ever since she got engaged, as expected, she's talked a lot about wedding plans, especially at our lunches. I know basically every detail. When she booked her venue she was really excited, but she refused to tell me where it was going to be, saying that she wanted it to be a surprise when the invitations came out.
The wedding is two weeks away now, and I've long since stopped waiting for my invitation to show up. I know when they were sent because she told me all about delivering them, and shows me every day the gifts people have started to buy off their registry.
I feel silly for saying it, but the more I think about it, the more hurt I feel that I haven't been included. It's a big wedding, and she has invited some other people from work that I didn't know she was even close to. She hasn't mentioned the reason why I'm not invited, and at this point I feel too awkward to ask. I guess it's just a slap in the face because I really thought we were close, and now I'm realising that maybe we're not.
The trouble is, since all this I've started to really examine our friendship, and I'm wondering if she even cares about me at all. I can think of a hundred examples of where I've helped her work through decisions, listen to her vent, stood up for her when she's had issues with colleagues etc. Even tons of little things, like if anyone brings in cake and she's out of the office I always save her a slice so she doesn't miss out. But I can't remember a time that she did anything for me in return.
Now when she talks to me, I've realised she doesn't even listen to me. When I'm finished talking she just carries on with what she was saying before, almost as if I'd never spoken at all. If we're ever talking about me or something I've been doing, she never has anything to say. She just kind of nods and then switches the conversation back to herself.
I'm starting to think she couldn't care less about me, she just likes having someone around who she can talk at, and whoever that person is doesn't really matter to her.
I've invested so many years into this friendship, it's really cut me deep. I feel used. It's also made being at work incredibly lonely, because she was my only friend.
I've stopped having lunch with her and any time she tries to chat I politely bring the conversation to a quick end and go back to work. She doesn't appear to have even noticed.
I do still wish her well, I'm still glad for her that life has turned around and she's so happy, but I'm a bit lost. I'm not sure if I'm being too harsh because I'm hurt, or if I even have the right to feel hurt in the first place, as I know weddings have a finite number of guests and you have to leave people out that you would invite in an ideal world.
But I'm not sure there's any way back from this either. Has anyone else had a similar experience? Am I being unreasonable or overdramatic? Should I just let the dust settle and see how I feel then?
TL;DR My best work friend didn't invite me to her wedding, and since then I've started to question our entire friendship. I think it's permanently damaged everything we had, and I'm feeling really hurt, lost, and unsure of how to proceed.


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