OP
I really don’t think you should take on all the “blame” for this friendship fizzling out. You may not have got it 100% right, but at least tried to do the right thing. Your friend has been unkind, used you when she wanted something from you and then dropped you again. That is not even trying to be a good friend but getting it a bit wrong- that’s just being a poor friend.
I had a friendship which fizzled out due to very similar issues. Sometimes it’s best for both of you to let it go, if it’s run it’s course.
My former friend actively tried to cut out a mutual friend from meetings/chats of a small group of friends because mutual friend was pregnant whilst she was struggling with fertility issues. She took badly when we wouldn’t- we agreed we’d do things separately with her if she couldn’t be around our other friend but that it wasn’t ok to try and cut our friend out of group things. She kept in contact with some of the group and not others for a few months, which was fine- and it all seemed to blow over for a bit.
Then, after a mc (which I know was excruciatingly painful for her, as I was personally very supportive and did a lot of listening/practical support) it deteriorated again. I was frequently accused of being thoughtless or unfeeling, as were others- e.g. mentioning our children was “too much”, even saying something like “sorry can’t come to x because of childcare ” was met with horror. I once picked her up as a favour- driving an hour and a half round trip to do so at very short notice (as in “can you come to x now)- but because I had left a child seat in the back I was “rubbing her face in the fact I had a child”. It was like we were expected to pretend that our children didn’t exist. I could understand not wanting to hear about them constantly, be expected to be surrounded by them at every meet up or go to child friendly venues, surrounded by children etc, but it went far beyond that. She would get upset if we met up with the children, but without her, and did not tell her. If we did tell her, that would upset her too.
It got too much, eventually- I was always second guessing what her reaction to things would be and it became exhausting. I acknowledge that sometimes I got it wrong, but equally, so did she. When I was pregnant with my second, she did not take it well and was quite unkind in her reaction. She tried to get the friendship group to leave me out of things as she didn’t feel she could be around me- surreptitiously at first (e.g organising things but not telling me- friends would often add me in to the group message or ask her why she hadn’t invited me or as, me why I couldn’t come to x) but when that wasn’t successful she basically asked them to leave me out if the group “until she could manage” and was quite unpleasant to us all- but me in particular- when nobody would agree. She didn’t get in contact for months. Then did contact me when she needed help with something within my professional expertise. Once she had got what she needed, she proceeded to ignore me again. It was the last straw. I could accept that she was hurting and finding things difficult. I could accept that she couldn’t cope with having much to do with dc. I could ignore periods of little contact and some of the barbed comments. But the rest? Nope- that was selfish, unkind and, ultimately, quite controlling behaviour. I just let it drift- if she was part of group messages or at mutual gatherings then I would be nice but I did not contact her directly.
The friendships fizzled out- there wasn’t a big argument or falling out, it was just that the friendship didn’t seem to bring her much happiness and certainly brought me more angst and irritation than pleasure. It was a shame because prior to that issue she had been a lot of fun, interesting, gave good advice, was generous with her time etc.
Her friendship with others in our group also drifted- again, neither party seemed to be gaining anything out of continuing them.
She did eventually contact me- I think initially wanting to restart the friendship. It was a bit odd- she accused me of cutting her off when she needed friends and then said she wanted to try to be friends again and “give me another chance” as she missed “everyone”. I said I had tried to be a good friend but that our needs had become completely incompatible- I had children and wasn’t prepared to pretend they did not exist, for example- and that some of her behaviour had been both hurtful and infuriating. I had assumed from her lack of contact that she did not to be close friends in the way we were before. She felt that I should have been “more understanding” of her pain and given her more leeway and time- I pointed out I, and the wider group, had put up with it for several years to varying degrees. I held no animosity, but that the friendship seemed to have run it’s course as it had been bringing little pleasure to either of us. She was quite taken aback, I don’t think she’d really stopped to consider the impact of her behaviour on others. I don’t see her often, but when I do I smile, say hello and am polite. But sometimes there is no going back to the way it was.