I've name changed for this post.
I'm sorry you're going through this OP. It sounds so emotionally upsetting. As others have said, it seems that something has happened for her (not necessarily something major or life changing) that has meant your friendship just isn't what she wants any longer. It isn't/doesn't have to be a reflection on you, but this doesn't stop the feelings of missing her and wondering why what you thought was a lifetime of friendship can be stopped just like that when you'd never dream of it.
One thing that others have touched upon that I agree with (albeit not from a perspective of understanding!) is that 'ghosting' is quite often recommended when it comes to the end of romantic relationships. 'Taking a clean break' is seen as the done thing, by protocol. 'Don't be friends with exes, leave them be to get over you' 'Don't ask him/her for explanations-concentrate on your healing, their loss!' etc.
A friendship is a relationship. Of course it isn't that you'd go on dates, raise children, have sex. But it is a relationship with another person with as many similarities (or more!) as differences to a romantic one. You go out together, support each other, share time/space/activities, appreciate one another, help one another through life-yet we're taught ghosting isn't the done thing here when that ends.
Along these lines, I've not ghosted anyone, but I nearly have.
I have a friend whom I met online about 12 years ago. When I say met online, it was a hobby group (think walking group) so not 'designed' for online activity more so meet ups for similar interests. We met up as a group not long after this and as meetings continued obviously you kind of sidle off into little groups or twosomes of those you click better with.
And us two really did. We're both gay women. We were both from the same county (in fact our shared accent was what first became noticeable to one another!) although living in a different place (where meet ups took place) at the time. We learned that we both grew up in the same town, although I live quite far away from her now.
Over time we exchanged numbers and began to talk on the 'phone/video call a lot, we both loved nature, gardening, dogs, many other shared interests and things in common. We had the same (rather warped!) sense of humour and had many shared past experiences. I am making this sound almost whimsical and it wasn't like that at all-we didn't think it at the time, it wasn't ever discussed-we just seemed to click and enjoy one another's company a lot and I guess much of it was due to common ground.
I was in an awful relationship that was just about ending, at this time. I hadn't told anyone at all about how awful it was, I'd kept it all to myself. I was still in the closet to my family at this point so couldn't talk to them-and felt too silly to speak to friends who I'd known longer as I'd always implied all was fine.
This woman however hadn't ever liked my partner. She was rather intuitive and had picked up the difficulties I was going through although I hadn't said anything. I was very wary of confiding in her too, I was worried she had an ulterior motive. She continually quizzed me about things until I broke down and told her. She assured me she thought a lot of me but wasn't wanting anything from me just wanted to help.
It was a very difficult time. There were ex's (teenage) children involved , ex was physically and mentally abusive and SS became involved. I had a very stressful job in safeguarding and I'd wake up in the night learning one of the kids had ran away, ex had left again or there were shouting matches-I worried I'd lose my job-and friend got me through it all, and it was such a painful experience that I don't know how I'd have coped without her. I was and always will appreciate her for this.
It wasn't just one-sided. She had a very difficult problem involving family not long after this which I supported her through gladly. She was afraid (justifiably) and upset. I admit, I think she's been more there for me than the other way around, she's generally just a stronger, more independent person who's had a much harder life. But still, the laughter, support and enjoyment continued and we supported one another ongoing with various things too.
I did notice a controlling element to her however. It was as if whenever I didn't need her support, when things were going well for me, she didn't like it. She'd try to drag issues out of me that weren't there-if she rang and asked was I okay and I said yes I'd get a lot of 'Are you sure? You're not! Tell me what's wrong!'
About a year after my awful ex left me, she (ex) came over to get all her things out of the house we'd shared that I was now moving out of. Things were calm with ex and I now, her children all okay. I was very much looking forward to this, a day of closure. My friend was ringing me constantly, sending me shitty messages and passive aggressive ones 'hope you're having fun' 'You forget about me when she's there' etc etc. It made the day awful for me, a day I'd been looking forward to. This has happened more than once in several different situations. E.G once I was feeling better I went out with some friends and she rang me and hung up on me because I'd not told her where I was going and she was hoping to talk to me that night-obviously I didn't realise I was 'meant' to.
I am in a different relationship and have been for some years now. I almost 'ghosted' friend when I confided in her that I was having a few difficulties within this relationship. Her response was to tell me she's in love with me and I should be with her instead.
Not a nice thing to do on my part but I became very upset. I hated the thought that not only was I in a bad situation again, but I was also hurting my friend who I loved to bits.. I didn't find this easy to cope with. Friend took this badly by expressing that every time she opens up about her feelings, people take it negatively and I'd just done the same. I said 'But Jane, I am in a relationship? And we've been friends years-surely you know I don't feel that way about you and that I won't react how you want by dumping Sue and running to you? What good can come of you telling me this?' I didn't understand why she didn't know that.
She'd also around this time often 'need' me while I was with my partner. If I didn't speak to her for a few days she'd guilt trip me that I'd 'abandoned' her while I was 'out enjoying myself'.
I honestly thought for a while that it would be kinder to ghost. I couldn't give friend what she wanted from me, I don't feel attracted to her and I don't believe we'd ever work as anything other than friends. I was wary of confiding in her ( I obviously didn't' speak about my relationship again), thought perhaps if I cut her off she'd get over me and be able to free herself up and not focus on me any longer.
I haven't done it and we've muddled along okay. But there's an elephant in the 'room' and I often wonder if I shouldn't have just cut her off for her own sake as well as mine.