@AwesomeFishsticks I've read all your posts (not all the responses yet though) and your situation sounds very similar to my own upbringing.
My mother left me in the care of someone else, who loved me as their own, whom I loved in turn - more so than my mother in some ways because this person never left me. Never abandoned me.
I say abandon because at times, that's what it feels like, even though rationally I know my mother did what she thought was best for me/her/our family and she left me in the care of a wonderful person.
But I can't help but feel as though she did abandon me, and since having my own children I can't imagine how it's possible to separate yourself from your own child; or given that she did, how difficult it must have been for her.
We were reunited after several years and spent the rest of my childhood together. But I can't "get over" this early childhood separation. Reasonably, like you, it feels as though there should be nothing to feel negative about. Emotionally I can't let it go :(
Which for me, is absolutely pointless and futile. I've thought about therapy for myself, but I'm ashamed to talk about this IRL - it's hard to say "my mother left me" because what would that mean? I was a bad baby? Not worth bothering with? That she prioritised other things in her life, rather than me? I know that's not what she thought but her actions... Rationally I can explain and justify my mother's actions, but emotionally this is baggage I'll always have.
Perversely I do not hold my father to the same account, even though he was far more absent during my childhood than my mother. I see the unfairness and sexism of that, I see my own feelings about being a mother myself reflecting back on my mother's choices and judging her for those. And I accept that my judgement is not fair on her, because she lived a very different life from mine, faced with difficult and hard choices that I have not had to deal with.
So I'm back to judging her, but knowing that I shouldn't judge her. I feel bad about certain aspects of my childhood, but I shouldn't really have reasons to feel bad :/
If you have some therapy to talk this through, I hope you find some closure and satisfaction 