Man has invisible demon following him that turns visible when eating people

Question

I read this book in 2007, it was written in English. The story revolves around a man who has been cursed (I think) to have a demon follow him.

The demon is normally invisible and the man is the only person who can see the demon. When the demon feeds or kills people he changes shape to a huge creature and becomes visible.

The demon is also invincible. I think I remember the man and demon talking about a time when the man tried to kill the demon after being cursed but the demon just came back.

It's quite a graphic book, not fit for children. It contained swearing, violence, sex, and possible drug use. I'm not sure if it was part of a series or just a single standalone book.

There are three scenes I can vaguely remember:

1. The man and the demon are in a bar. The man is playing pool against a bar regular who is apparently the best pool player in town. The man isn't too good but the invisible demon helps lead the balls into the pockets (insane shots like a ball curving 90 degrees). The regular gets mad that he lost. The man and the demon were playing pool to get money (for what I can't remember)

2. There was a scene where an old man is telling his friends about the night before: He wakes up in the middle of the night and tells his wife "The bear is out of the cave" or something similar. His wife just rolls over and says "You better put some ice on it". This story was alluding to the man wanting to have sex with his wife for the first time in ages, but she was not interested at all.

3. I remember a hospital being destroyed when the demon goes crazy and needs to eat. The love interest might have worked at the hospital.

I will add more details if and when I remember them.

Answer 1

Possibly Practical Demonkeeping by Christopher Moore.

In Christopher Moore's ingenious debut novel, we meet one of the most memorably mismatched pairs in the annals of literature. The good-looking one is one-hundred-year-old ex-seminarian and "roads" scholar Travis O'Hearn. The green one is Catch, a demon with a nasty habit of eating most of the people he meets. Behind the fake Tudor façade of Pine Cove, California, Catch sees a four-star buffet. Travis, on the other hand, thinks he sees a way of ridding himself of his toothy traveling companion. The winos, neo-pagans, and deadbeat Lotharios of Pine Cove, meanwhile, have other ideas. And none of them is quite prepared when all hell breaks loose.

The TVTropes page mentions the pool example:

Calling Your Shots: Travis cheats at pool by having his invisible demon, Catch, move the balls where he calls them. Usually.

Google Books mentions the bear:

"I tried to wake up the wife. Whacked her on the leg with it just to get her attention. I told her the bear was charging and I have one bullet left."
"And?" Brine filled the pause.
"She told me to put some ice on it to make the swelling go down."

Found with a search for book man followed by invisible demon