My friend who lives with me seems to be declining. He's no longer paying bills, driving, and often leaves the gas stove burners on.

Once these behaviors start, they don't stop. It's reasonable to believe that he has dementia.

It's an unpredictable disease and eventually fatal. You can't cure it, and if you stick around, you will eventually become responsible for this person.

Is that what you want? Time to decide now.

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I bookmarked this ages ago, hope it helps.

You need to get your friend to a Neurologist to be evaluated. He is showing signs of Dementia. Then you need to decide what you are going to do if he is formally diagnosed. He is going to need care and since he is leaving the stove on, he is probably already 24/7 care.

It all depends on what kind of "friend" you are. If he is just a roommate sharing expenses I don't know if I would take on his care. It may be time to get his family involved to figure out what they can and can't do. If your very close, like a couple, then u need to figure out if your in for the longhaul.

First he needs to be evaluated and then you will need to make some decisions. When that happens think about what you are willing and not willing to do. Dementia is not some little old person sitting in a rocking chair staring at the walls. Dementia is very unpredictable. At this point, your friend should not be left alone.

A few questions..
How old is this person?
Any other medical conditions.

Have you actually talked to him about the bills, about his driving about leaving the stove on?

Leaving the stove on, once could be a case of getting sidetracked and forgetting you had the stove on.

Is he not driving any longer? If so why. Could be a lot of reasons. Cant afford gas, can't afford the insurance.
Is he working? Were hours cut so that he can no longer afford to pay bills? Or pay for gas, insurance?
If the driving issues are that he is still driving but is no longer driving safely that is a different matter. (Gut response to this question...Would you let your kids or grandkids ride in the car with him? If the answer is no then there is a problem)

Does this man have kids? Are they involved? Have you talked to them about your concerns?
The big question here is ... How involved to you want to be if he is diagnosed with dementia? Are you prepared to be a caregiver?
Are you financially linked? If so you need to protect yourself

By the way...there are knob covers for stoves that will prevent him from turning the stove on. Or remove the knobs if you are able to. Or if there is a single breaker switch to cut the stove off you can flip that switch but that is a bit of a pain for you every time you want to use the stove. (An electrician could put in a switch that would be easier for you to get to.)

Decline? Depression? Delerium?

Sometimes 'brain fog' can come with UTI, chest infections, Covid.

Would your friend be open to a checkup with their Doctor? Maybe with you as support? You could subtlety mention you had some 'concerns'. Keep it vague or detailed as you think best to keep your friend's trust & get some issues ruled out.

Bumping this one up to be seen and answered.