Feeling like an afterthought in my own family

when I say I'm "the black sheep" of the family, I don't mean I'm the weird outcast, I mean that I'm usually an after thought, my dad had two kids before he met my mom and my mom had one before she met my dad. between me and my next sibling, there is a 12 year age gap, my oldest sister is literally old enough to be my mom, my oldest nephew is three months younger than me. I came along as an after thought, my mom won't admit it, but I was definitely an accident that she wanted to keep, and my father was happy to have another kid, but my older siblings (on my dad's side) they loved me, and cared about me, but as I grew up, that kind of went away. I may be the youngest of four, but I was pretty much raised as an only child, my aunts and uncles reach out to my siblings, but I don't exist, they're happy to see them but are underwhelmed when I show up, I'm not asking for a parade and celebration just for showing up, but my own family leaves me behind. staying with my oldest sister made me realize that my presence is nearly unwanted, my own brother barely spoke to me when he came to visit, my aunts and uncles didn't reach out to see if I can come see them, and before you ask, I let everyone know that I'd be close by, and that o wanted to see them, but nothing even happened. I was the product of two families that damn near hate each other, and I'm left out of both. on the positive side, my husbands family showed me what it means to have a family that cares, my in-laws are excited to see me and my husband, my husband's uncle treats me like one of his own, my brother in-law welcomes me as family, and I reciprocate. I'm glad I found a family that shows that they care, but I feel lost now that I've made the realization that I'm essentially a burden to my own blood family, what hurts more is that I always loved going to their houses and spending time with my siblings, aunt, and uncles, but now I barely exist, and that hurts.