My German Shepherd is very aggressive?

I currently have this 1.5 year old German Shepherd dog who is very aggressive. He has been aggressive since he was a puppy. He's very loving and loyal to me and my family, but not so nice towards others. He will pounce on the window and barks like crazy at anybody passing by our house, and he growls and flares... show more I currently have this 1.5 year old German Shepherd dog who is very aggressive. He has been aggressive since he was a puppy. He's very loving and loyal to me and my family, but not so nice towards others.
He will pounce on the window and barks like crazy at anybody passing by our house, and he growls and flares his nostrils if he hears someone outside. It's been so stressful because I can't even take him out now because he's very big and I will be dragged.
Last time I tried to take him for a walk with my cousin, he was trying to get to her and I was holding him back and his nails were getting chipped and sanded off by the cement to the point of bleeding.. but he still wouldn't stop (I use a muzzle whenever i take him out). One time my cousin went up to him while he had his muzzle on, he kept trying to jump and get at her face and was smashing into her with his mouth.
I do not think he's fear aggressive because he lunges at people and wants to bite/kill them. Usually when he's barking at someone, his tail is wagging.
When i let him out into the backyard to do his business, I have to tie him to a long leash because in the past he has bitten my neighbor's dog from under the fence.
He's not used to my Auntie so whenever she comes over, we have to put him in another room. But the thing is my dog has seen her numerous times but he is still aggressive towards her.

So I'm wondering how to help him to become more friendly and less uptight about everything.

P.s. He hasn't been neutered.. But i'm not sure how i can bring him to the vet without killing people..
Update: The comment stating that I let my dog act this way, well i usually say "No" or Pull his leash, and if he's dragging me on walks I walk the other way on purpose but then he just starts pulling again. Is that the way I'm supposed to stop him or let him know that it's bad behavior? because it... show more The comment stating that I let my dog act this way, well i usually say "No" or Pull his leash, and if he's dragging me on walks I walk the other way on purpose but then he just starts pulling again.
Is that the way I'm supposed to stop him or let him know that it's bad behavior? because it doesn't seem to be working.. and I don't have any ideas.
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