Problem with our bond, or just stressing over nothing?

Good day all,

My dog; 5 month old GSD (Faust)

When I first got Faust, everything was great, and everything is still great, but I am starting to wonder if his current mood is simply his independence coming out (which would be fine), or if there is an issue with our ‘bond’. This is probably just a first time dog owner stressing over nothing.

Our training is 99% positive reinforcement, the only time he gets corrected is from biting (while playing/running with my g/f, he would jump up and bite her on the ass… that’s a no-no) – other than that, there is no physical corrections, so I don’t think I am being to ‘hard’.

When I call him, he comes. When I pet him, he just sits there, no tail wagging… when I stop petting him, he walks away, lays down. I am probably just anthropomorphizing, but he always looks ‘sad’. We go for daily walks, I take him off lease and we play… but he is just ‘blahh’.

He’s healthy.

Is this something to do with his development/personality? Will he grow out of it? Or is there something (specific) I can do to help reinforce our bond (if needed).

I can tell he is very independent and confident, which is what I wanted in a dog (and the breeder, who I trust) told me he was (before I even told her what I was looking for).

Thank you

** Because everyone likes pictures **