A lot of what you mentioned sim, from the struggles to maintain a healthy diet to the self harm is extremely common among those in recovery, particular on the earlier side - men no less than women. What you're experiencing, given all you've been going through recently with the death of a loved one and the loss of your primary coping mechanism (opioids), is very, very normal. Shitty, yes, but hardly abnormal.
Doing super simple things, like forcing yourself to eat three times a day - it doesn't matter what, just pick something you love to eat, like a smoothie, ice cream/milkshake, burger, whatever floats your boat. You can work on improving the quality of your diet later on, as it's pretty easy to supplement tasty less than healthy nourishment for healthier but still super tasty nourishment. What do you "normally" love to eat?
Do you have a psychologist and psychiatrist you can work on your depression with? I take it your already have a psychiatrist, so perhaps you can start taking an antidepressant (again - every little bit helps, and our bodies change after withdrawal, so after a few weeks on something like bupropion you might noticed a different effect than last time you tried it).
How much exercise are you able to get these days sim? I know forcing one's self to do anything, let alone movement, when depressed seems near impossible at times. But forcing yourself to get outside for a walk, even if just a couple times a week (and have it lead somewhere where you can get yourself a little reward, like to the local coffee shop, grocery or restaurant) will make a difference. Especially if it involves you nature - I think you already know how passionate I am about this nature bath thing
Things will improve sim. They fucking such right now, granted, but life has a way of changing. Any small, little bits of progress you can make to help yourself continue moving in positive directions in your recovery, whether that is taking an antidepressant, eating three times a day or going for the occasional walk, doesn't matter. No matter how large or small, a step in the direction of a mentally and physically healthier you is a step in progress and a step in the right direction. You're already making progress you know, by simply maintaining abstinence. This is hardly enough on it's own, I know, but even this is you working on yourself to become healthier.
What are your sleep patterns like these days? Forcing one's self to maintain a regular sleep schedule of not too much sleep (so say no more than 8hrs a day, perhaps with a siesta in the afternoon) can also help alleviate depression. When I tend to get depressed I find myself sleeping way to much, which makes it more difficult to get stuff done or feel motivated compared to when I start the day off right at the right time. This may not be an issue for you, but our sleep habits have a significant effect on our mental health, so something worth reflecting on.
And honesty, who knows. Perhaps you will eventually come to decide complete abstinence isn't working out right now, and choose to go on a six month low dose course of buprenorphine to help manage your depression. It more enlightened places it is, at low doses, prescribed as quite the effective medication for severe depression. By mentioning this, I'm just trying to highlight that the end goal isn't abstinence per se, it is living a healthy, meaningful life - one that means something worthwhile to you - and at the end of the day, most of all you.
Keep you head up brother!