Maybe he's not crazy. if you've ever had a large black dog, then it's possible his spirit is still with you. lots of people see things that we can't.

It's Sirius Black.

This reminds of a dream I had about I move to London and was star of reality show and my friend told me to go for a walk and he would deal with the paparazzi and while I was walking I came across a black dog and I thought it was going to attack me but ended up passing me and attacking my ex bf the one who has been stalking me since we broke in 2001

Oh god!!!!! It's the-the-the..... The GRIM!!! I would get a new boyfriend though:)

A sixth sense is not uncommon. A black dog following you is a bad omen though it usually is a harbinger of death.

Big black dogs are the symbol for death.... And is usually associated with the Devil or a Hellhound.

The Grim..Taking form of a giant spectral dog. It's among the darkest omens in our world. It's an omen of death.

A black dog is from Irish lore, this dog would stalk its targets then devour them be careful

Don't worry, the dog is just a mass murdering wizard in its animagus form. He wont hurt you though, he's your godfather.

What if he's telling the truth ?