Hi Claudia,
Throughout my life I have given home to about 10 rescue dogs. You say your dog is loving. Go with that. Your dog experienced a lot of change in its life and probably lost hope of finding permanency.
In my experience these dogs are loving and easy to handle but it takes them about 2 months to look at you with love in their eyes. You only had your dog for a short time so give it time and be kind to him. Don’t worry about being the alpha, give him structure, train him and the rest will come as a result. He will love you and consider you as number 1 in his life.