How do you regain your motivation when life stress is destroying it

Let's just preface this by saying I don't have anything like your stressors, anymore.

Even so, I don't/can't rely on motivation, because that's just not my strong suit. Habits work better for me. Some folks here think in terms of the minimum habits they can sustain, to keep making progress (or at least avoid slipping backwards) when life gets complicated.

Can you rely on some repetitive cookie-cutter eating strategies (cycle of same/similar meals), for example, that you know will give you around the right calorie level for slight loss or even maintenance? (Getting plenty of fruits and veggies in there in easy forms could be good: Some micronutrients help counter stress effects. Apples, oranges, baby carrots, cherry tomatoes, etc.?)

One thing I'm pretty sure of: If the problem is stress, the solution 100% isn't food. The solution is better stress management.

Some amount of exercise perhaps can help. (Maybe mild exercise, so as not to add physical stress, maybe some short walks in outdoor air & light at intervals through the day, if you can fit them in? Or, conversely, some people find very, very short but super intense exercise to be a stress-buster, like exercise bike or similar with maybe a 3-5 minute warmup, a few reps (3-8, say) of 20" max effort 10" easy effort, 5 minutes cool down - if your current fitness level allows that without it being excessively punitive).

Consider meditation (there are apps for that now, it's not a woo-woo mystical thing, just a way to relax the body). If you're a person of faith, maybe prayer. Some people like journaling, even 5 minutes in the morning scribbling whatever runs through your head and out to your fingers, or simply writing down every day 3 things you're grateful for. If you have access, maybe warm bath, hot tub, steam room, sauna sort of thing?

I've been told (by my employer's counseling referral service, i.e., professionals) that there are cognitive behavioral therapy (CBT) interventions that are very effective for "racing brain" insomnia. (Haven't tried it, because I have a different type of insomnia, but did benefit from a credentialed psychologist for hypnotherapy for my insomnia type). These days, phone or telehealth consultations are available, and may be easier to fit in.

Clearly, you're going through a lot. You can still make progress, or at least hold the line, but you'll need to scale your expectations to the moment, and take your own personality/inclinations/strengths/limitations into account to keep it as easy as possible.

Don't be too hard on yourself: You're facing a lot. You can get through this, even if you find you need to take your foot off the accelerator for a while. Any healthy interventions you can still manage to accomplish, will help you get through.

Wishing you a calmer path ahead, in terms of external stress triggers!