This is complicated and I somewhat understand my parents' reluctance to accept my new (rekindled) relationship, but I also think that they are very unfair.
My former foster brother and I have found each other again, and have started seeing each other. He only stayed with my family for a few years when we were both young and we developed a pretty strong sort of relationship back then. Once my parents realised he was removed and it was obviously very upsetting for both of us, and also for my parents.
I was mad at them for ages back then but as an adult I totally understand that this was the only right thing for them to do. But I find their attitude very offensive. Since then they have maintained that he was abusive and led me astray etc etc etc, which simply isn't true. We were both children, about the same age, there was no age or power imbalance. I spent some time thinking about this as I went through therapy for a different issue, and I genuinely don't believe that he did anything bad or that he "corrupted" me in any way.
It was very upsetting when it all came to an end I know that he suffered more than me as he was uprooted again and ran away trying to come back a few times until it stopped. When we reconnected he told me that he had sent me letters but that he never got a response and stopped after a while. I asked my parents about this and they confirmed that I had gotten letters but that they had thrown them away to let me move on.
We're both adults now, and the situation is obviously completely different, but my parents were abhorred when I told them that we had taken up contact again, and they keep bringing up these abuse and violence allegations and other stuff, and I got really mad at them earlier but I also feel guilty now.