OP - you sound wonderful and I don't think there's anything wrong with you - I think your expectations of friendships may be a little bit high?
Many friendships are only superficial or temporary or situational.
I used to be a bit like you in my 30s - trying to organise groups or contacting people 1-1. My WhatsApp was full of "dead groups".
Looking back, I probably came across as intense and needy.
I'm happy with myself, but British culture is super emotionally closed/conservative when it comes to new friendships.
I'd say this is even stronger for female friendships.
If your face doesn't perfectly fit, or you secretly trigger someone you're completely "shut out" and it's easy to take personally!
You make someone in a group competitive or judgemental or upset the unspoken hierarchy....that's it!
No point analysing, it happens often in groups.
Plus many Ok people don't tend to cultivate new friends due to moving about, changing jobs, changing life stages, prioritising family, burnt out from work. Or they're traumatised from managing previous friend drama.
You can't tell someone's private situation.
I love meeting new people but can't prioritise close friends as work is challenging.
I'd hate to have a good chat or connection for someone to feel I'd rejected/ghosted them. But work and money are the (secret) priority for me.
For the loneliness, maybe think about self-care plus networks or communities?
I'd say to find organised regular hobby groups and third spaces and commit to regularly physically turning up with no expectations.
(Meetups, sports, coworking spaces, Buddhist meditation or Quaker groups, hiking groups, book clubs, Shut up and Write).
Try a few and review, then make extra effort with the good ones. This will take time so keep a sense of humour.
I personally have tried to make myself schedule in and try out 1-2 new groups/spaces each month. This has been a slow process, about a year?
A few were "ok but not super sociable". Or too far or not practical for me to continue attending etc.
Two had crazy women who were bristling on first look and it didn't get better 🥺
One meet advertised for thirty somethings was all elderly men 🫣 and me (note I look young for my age). It was actually a fine conversation to be fair.
One running group had no-one but me attend, but I had a plan B (Aldi shop nearby).
If the group is "ok" and some regulars and some new and solo people and they move around to chat, that's a good sign.
There's often some "harmless regular group weirdos", but if there are enough ok people don't let them put you off.
You may find a lot of retired folk or people new to town. International people bemused at how unfriendly the UK is 😉.
I find mixed groups easier as men are more comfortable coming solo and talking to everyone.
Just observe and be open to see what happens rather than looking for phone numbers straight away. If you're not comfortable, try to work out if it's the group, or your own anxiety.
It can take a couple of meets, or towards the end of the night for people to relax.
(Somewhere where you're the only newcomer....and no-one at all talks to newcomers is definitely a NO!)
It's been a longer term project with lots of anxiety and weird experiences (and some great ones!). I journalled in DayOne to process my thoughts and work out what to continue attending.
However has definitely paid off - before I'd write things off too easily (and I enjoy staying in so too easy to opt out!).
Now I've taken the time to sift through, I've found 3-4 groups I'm happy to be a physical regular at and seem to be booked out till summer.
Can't go all the time but 3-4 groups means 1-2 things a month (with no organising pressure for me).
Before I was looking for deep, committed conversations and friendships and "too much too soon" and feeling rejected if it didn't work.
However, many friendships people have are actually quite superficial/small talk/just a chance to get out to a pub - nothing wrong with that.
People can be amazing on an ad-hoc basis, but looking for "ride or die" friends is too intense and seems to only attract weirdos or predators.
Realistically, most people only rely on partner/family/themselves for commitments/important stuff.
Now I'm treating it more casually and have lower expectations it's more emotionally enjoyable and feels less dramatic.
I may ultimately have deeper connections develop, but I know I have an ok amount of organised contact either way (and am not turning into a complete weirdo writing long posts on Mumsnet ALL the time)