opinions from adult adoptees

Hi all, I am an adult adoptee and I am in the midst of dealing with being in contact with my birth family. I have had a very difficult time as my birthfamily is unhealthy and they are VERY selfish people. I have been hurt a lot by them emotionally over the last year and a half of contact with them. Specifically from my birth sister. And it's affecting a relationship with someone in my life that i met at the same time as my biological birth sister. this person came into my life at the same time as my birth sister and it's ironic because this person and i got really close very fast and she started assuming the role of my big sister when my birth sister, who is actually my sister treated me terribly. But as I kept having conflicts with my biological sister and birth family it began to affect and is affecting my relationship with this person who is like a big sister to me. I distance myself from her and feel completely unworthy to have her in my life or have her care for me. I don't know why she would want to be my big sister and it's really been affecting me and our relationship. it's not fair to her at all :( I am needing some opinions of other adult adoptees...can someone shed some light on this for me....i'd really appreciate it. thank you