My best friend passed and now his dog is reactive…. What do I do?

So my (now) dog used to belong to my best friend who passed back in November. He had this dog, Benji(5yo Pit Bull), since Benji was only months old. Benji has been around other dogs and lots of different people his whole life.

He has not ever been aggressive or excessively barked at anyone or anything. My best friend passed away while he was not home and Benji never got to see the body. Benji stayed in the house with my friend’s roommates for about a month with the other dog my friend had until we decided it was best if I took Benji because I’d known him for a long time.

I have 4 cats and we were able to pretty easily introduce Benji to the cats, although he already knew two of them prior. But for some reason Benji is now very territorial over me and will not allow other dogs or people around me. The exception is if I know a person he acts completely normal, even if he’s never met them. It is only when I don’t know a person or he previously knows a dog that he is okay with them.

He used to walk great, now he pulls and tries to attack other dogs. Our new roommates have two dogs that he has attacked and he won’t let any strangers near me. I don’t know what to do and this just seems so complex. He’s very attached to me, I think to him I’m what’s left of his owner. My boyfriend and I are about to start trucking and we want Benji to come with us, he loves the car. I don’t think he would ever hurt a person but it is just so stressful and painful to watch him be so reactive towards other people and dogs. Please, any advice would be greatly appreciated, not taking him on the road with us is not an option. I will not let this dog feel abandoned again.