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

Original post
So it took me a few days to decide the best way to approach this, but yesterday I had lunch with her again and had the conversation.
I started by saying: "So you've sent all your invitations out now, haven't you?"
She looked immediately panicked by my question and I knew right away that she didn't want me to go down this road.
When she said she had sent them all, I asked if that meant she could show me her venue now.
She showed me the website of it, including the photo gallery, and talked me through all about where everything was going to happen, all the flowers and decorations she was going to add etc. It's a nice enough country hotel with some pretty gardens, but I'm not sure what all the secrecy was for.
I probed a little more, asking who she's invited from work (the list didn't include me), said I was looking forward to seeing the photos so I could see how everything looked (she didn't correct me that I would see it on the day) and then I was completely sure that my lack of invitation wasn't an accident. She looked so relieved when I switched subject and asked if she's excited about her honeymoon and having a rest from all the wedding stress.
So I'm definitely not invited. I thought it over carefully and I have decided not to ask why, for three reasons:
1) The reason is already fairly obvious. She clearly doesn't think we're anything more than colleagues and I've misread the situation. (There were some other theories suggested e.g. jealous husband-to-be, associating me with her past grief, but considering everything I know about her and our history I'm sure it's not that.) I'm not sure why she didn't cool it on the wedding talk with someone she had no intention of inviting, or even just bring it up with me and explain why I'm not invited, but never mind.
2) Having an awkward relationship at work is the last thing I want. I'm worried that if I push this and turn it into an "issue" that I'll look pathetic and needy, or it will just be unprofessional. I also run the risk of her badmouthing me to colleagues and mutual friends, and I will find it much easier and less messy to handle my own feelings quietly.
3) This is a once in a lifetime experience for her, and I don't want to be the source of drama that dampens her spirits at all. I'd rather just let her enjoy her wedding, make good memories and not bring her down.
And you know, I'm fine with not going. It was never really about getting invited to a wedding, it was more having to face the fact that I'd been naive and taken for granted, and I felt silly that I'd invested way too much in this relationship. That's not all on her, because she was never obligated to be my friend.
Talking it through on my previous post actually really helped me work through my feelings. When I went back to work on Monday I felt much calmer and more detached from it emotionally.
I have looked back on our whole relationship and honestly she's always been self involved, entitled and narcissistic. Being a bride has just made it more obvious, but it's always been there. She's also never given back to me (besides helping me get my job, which of course I'm grateful for), in that she's never been willing to talk me through any problems I've had, and although I help her happily with her work, she says no if I ask her for help in return.
She has a few office enemies and even though I saw her negative traits that caused her to be disliked by some people, I overlooked them and defended her anyway. Now I have put a little distance there it's quite apparent that she's not a very nice person, and I'm genuinely OK with just moving on.
She hasn't really noticed the distance between us so far (or she has noticed and doesn't care/is relieved that I'm giving her space), so I intend to just continue with doing that. If she eventually asks why, or I get the sense that she's trying to rekindle our friendship, then it will be time to clear the air with how I've been feeling. If she doesn't and we just continue drifting, then that's probably for the best.
It's sad to lose a friend, and it will probably take me some time to get over it and to become comfortable with the change in our relationship, but I have other genuine friendships, and plenty of colleagues who are lovely people who I can get to know better now.
The main thing I really took from my original post, and I'm so glad I did post because I needed some tough love on this, is that my fear of confrontation really needs dealing with.
If I can learn how to better speak my mind as things are happening, that will stop things from building and building until I have to have a Serious Conversation and it makes what should have been a molehill into a mountain.
I also need to figure out how to have difficult conversations without having an anxiety attack, which not only weakens my message but is extremely distressing and puts me off dealing with things and being honest with people.
I had a couple of books on assertiveness recommended to me, so I've bought them to start me off. I'm also looking into going to a coach, or maybe a couple of therapy sessions at least, to try and better myself. I don't want to hurt other people by doing this, so this has become top priority for me.
Thank you so much everyone who pointed that out to me. I was aware of it but I didn't think it was a problem and figured I'd just be that way all my life. Now I know better. Thank you for being so honest with me.
Also thank you to those who talked me through the one-sided friendship issue. I'm a good listener and have always attracted people who need to vent, but I only ever noticed the one-off conversations, and didn't think I was being taken advantage of as a long term listening ear.
I have been examining my other friendships in the last few days, to see if anyone else is using me in the same way, or if I've even been doing this to others and not had the self awareness to realise. There are a couple of changes I need to make, including a friendship that I need to set some boundaries in, and another one where I've not been giving back to the other person as much I should have. I have learned a really valuable lesson from this about maintaining healthy relationships, and I'm very grateful for that.
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TL;DR So I'm definitely not invited, our friendship is likely over (but that's actually OK) and I'm going to work on my assertiveness so I can handle things like this better next time. I'm also going to move forward having learned a good lesson about friendships being two-way.
Edit: A few people have been asking about the books I was recommended: Nonviolent Communication by Marshall Rosenberg When I Say No I Feel Guilty by Manuel J Smith Why Men Love ******* by Sherry Argov


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