Am childfree myself
The problem sounds like you seem to be desperate for a relationship that you will accept anything in order to have one.
- Denying yourself experience of parenthood in multiple relationships with men who said they didn't want kids. Now arguably time has basically run out for you.
- Allowing someone to move in with you after a very short timeframe (blame covid but it seems like you'd have allowed them to shack up with you regardless of the pandemic)
People don't respect those who have no backbone or will do whatever it takes to please you.
Someone who has standards, boundaries, their own goals/dreams is more desirable.
Right now you seem willing to put a man before your own needs & wants - likely they meet another woman who knows what she wants out of life, has the ability to say "no" and this is more attractive to them - confidence is attractive. Telling people to jog on is attractive. Having your own fulfilling life is attractive.
Your problem is you will change yourself to suit whoever comes along, even to the point of denying yourself the opportunity to be a mother. Your desperation is almost without a doubt turning people off.
This is why you feel like "the one before the one"
You're trying to make all these blokes "the one" for you - without having any dealbreakers about what "the one" means for you you. Maybe that's a man who wants a family, or has his own career, or whatnot.
You will accept crumbs, but now confused as to why that's all you have on offer.
You have shown people how to treat you.
Think about what you want & need out of your own life & stop thinking a man is going to complete you. If you want kids you need to look at a donor now, or accept you have missed that boat due to prioritising other things.
For me children are a dealbreaker in that I will not be with someone who wants to start a family. But it sounds like you did want that, but gave it up for people who were not actually "the one". You moulded yourself to try and make yourself the one for them & that will always backfire.