Hi Alacarte,
I would tell your relative that compromised mental health can come about for a huge number of reasons, some of which don't involve any kind of substance at all. Sure using a substance as a way of distracting ourselves from the harsh reality of what's really going on inside of us helps keep us trapped, but IMO substance abuse is not a cause but almost always a bi-product of compromised mental health. A coping mechanism of sorts.
Why do we drink or smoke weed? Just to feel 'good'? If our sober life is that boring (or painful) that we need a substance to feel whole, relaxed, happy etc.. then surely that points to something deeper than getting drunk or blazed for the hell of it?
As someone who used anything they could get their hands on to mask and distract from pain for a long time in my youth and most of my 20s I have only recently really fully understood what was going on here.
I would try and explain things this way to my relative if I were you.
As for work. It goes both ways. You should get a good vibe about the kind of work place you're interviewing for at the outset.
Does the boss come across as someone who has an 'open door' policy, as someone who can be trusted and is empathetic?
If not, it may not be the right fit for you. Only you will be able to tell and it will come down to how high on your 'wish list' that quality will be in a prospective employer.
If you are quite self aware and honestly know you are struggling right now or have been for some time, this may even be more of a priority than $$. It's encouraging to hear about some employers taking mental health more seriously and work/life balance, working from home etc.. where possible but I still think this is the exception more than the rule.
Best of luck.