I don't want to seem mean but I don't think the mother is interested in you in the slightest and invites you only through a misguided sense of kindness and not wishing to be rude, or maybe she is scared of being left lonely , in which case you are taking advantage by hanging around when you have been brushed off (first politely but now increasingly rudely).
As you say, the relationship was never going anywhere much in the first place and now you have made a stand by making her choose between you and her child, she has gone for the sensible option in sticking by her daughter. Also I cannot help but suggest that some of the daughter's mocking is inspired by things she has heard her mother saying. Maybe they see you as weak as you didn't offer any stability. Maybe you pose a threat to the current family balance, and you are not spreading joy by any means. There are plenty of women in the world so don't make two (at least) feel uncomfortable and unhappy in their own home.
Naomi is an adult now and if her mother prefers her company to your own company, then you will have to accept this. It's not expected nowadays for kids to leave home as early as they used to in life and maybe her mum loves her with all her warts and all (of course).
I have to say that I used to have a similar friend who just used to turn up with very little left in common, who expected to sit in front of the tv and stay for hours, when a simple hour or two with no expectations might have been pleasant, or even out of the family home for a change, as Brenda says. I know this will sound harsh but you have to move on, and leave yourself with some dignity and tact.