Kept/adopted sibling dynamic

One of the many things my big sister and I share is a fear of loss. Even if the loss would be a positive one, it should be avoided at all costs. We hold onto relationships and friendships long past their expiration date, and as a general rule, under the surface there seems to be a feeling of "well, its sucky, but something sucky is better than nothing". I wonder how common our issues are, if its a dynamic seen a lot in kept/adopted siblings. We feel the way we do for different reasons, but it all seems to center around the choice our mother made, the choice to keep her and relinquish me.

I can't seem to find much of anything in regards to grown, reunited siblings. There are some tidbits on animosity in between kept/adopted siblings as related to the attention and love of the first parent, or birth order changes, but I seem to be at a loss of finding anything informative about relationships in adulthood between siblings separated by adoption, and navigating that reunion. Most of what I'm finding surrounds how adoptive parents "should" handle the issue of biological siblings...Knock on wood, we are doing ok, but it would be nice to be able to track down some info on others in our situation. Perhaps I'm just not keying in the right search words!