Fathers have a really tough job in our society already. They have many expectations placed on them, yet have limited abilities to enforce anything they do and are often not supported when making the harder decisions.
This is even more of an issue for adoptive dads. It is quite easy for his children to reject him, instead desiring a "perfect dad" vision they have in their minds. At least that was true in my case. Ironically, my children's birthfather helps them do things that are very destructive to their life. My wife and I tried to teach them to restrain their impulses and that is now being actively undermined.
It is not surprising and many children rebel against their parent's rules when they become adults, yet factoring in a birth family makes it even more challenging and an extra way to reject the parents.
Happy Father's Day to the true fathers! May you find something to anchor yourself to whether the rejection!