transitions

I'm a new foster parent, single, have had two placements so far, one for three months and this one for almost ten. Each arrival was very abrupt, as was the first departure. This one, however, is transitioning to a new foster/adoptive family to be with siblings. Without saying too much, I'm just torn up with worry... even though they are wonderful people, and I'm a worrier by nature. He has some behavior issues (not too severe, but still...), which are not happening there, but have happened in each other placement as well as in my home, at daycare, and at district preschool. I know being with siblings is the right thing to try, I just worry about him getting the positive attention, and I'm frustrated about all the hard work he and I have done to bring the good changes in his behavior, which doesn't seem to be being recognized. Any advice on how to deal with this frustration without letting it take over? I have supportive friends and family to talk to, but I think they're getting tired of hearing it over and over each time someone says something that sets me off again (in my head... not in front of him). jan