I relate to this post quite a bit - but not so much in infantilization, but its older sibling learned helplessness. Deep down I feel like when I cut ties with her that there will be no one in my life that I can trust to support me (and I dont mean financially - I mean emotionally, with encouragement) yet its quite a paradox, because she does not support me in any way, never really has, she consistently undermines me to keep me dependent on her (mostly emotionally) at this point. I've tried many times to break away from her (I'm almost done with her now) but always have this haunting feeling inside, kind of like something you'd be afraid to throw away, because while its not perfect, if you can't get it back - its gone forever and you might need it one day.
Rationally, I can look at all that I have done and overcome in my life already, but I am alone (single) and I've never had the person behind me to back me up (on my soulmate list is #3 - assertiveness, can understand, accept my NM and back me unconditionally when necessary) so that last tie is very hard to cut, but I know its necessary.
Part of my trust issue with others is that I don't feel safe, I don't feel supported and I don't feel assertive enough myself to protect myself and boundaries.
Its part of why I'm still single ....