I’m sorry to hear you’re struggling with your work situation. Four years is a long time, but I’m sure you’ll make it through if you keep working at it.
I’ve gone through some dark periods in my life too, and so I know how hopeless it can feel. I think it’s important to try to find something to work towards and feel optimistic about. Working towards that certification could provide that for you, even if it takes a long time to save up for the actual course. Building up your own fitness, while you aim to eventually help others, could also help. I know that, for me, accomplishing small goals in the gym is great for my confidence.
I hope it all work out for you!