Also 38, also married, also two daughters, also have depression.
I can't tell you what works or not for you but I can say what helped me go from suicidal over a failing business to functional enough to interview at 20+ tech companies and land a job I like.
I firstly spoke with someone. Dealing with depression totally alone is not easy. I don't know your wife (ofc) but if someone married you they (probably?) care enough to hear more than just good news from you. If you really can't afford to share with your wife then damn, that's rough, but do share with someone who knows your situation and can advise your doctor, a therapist, a parent, someone.
Deleting contacts on social is a symptom of depression. I did it and my counsellor raised it. Ask yourself if you'd notice if someone unfriended you first? It's not like FB notifies you. Your friends and family care, they do, but they also have their own lives and also let's be honest, a lot of people hardly check FB in depth these days anyways. No one is going to notice their friend list drop down by 1.
> I eat the cheapest fast food lunch alone
I'm gonna be dictatorial on this one and just say 'stop'. Don't do it. Junk food is a treat, like ice cream. You wouldn't incorporate ice cream as a regular part
of your nutrition.
> then it gets late and I have no more energy to do anything useful
That's true for any parent, especially those dealing with stress and depression. You're not alone on this one. I get done with the day after tucking my kids in and I literally have like 1-2 hours to maybe learn something tech related to advance my career or veg out with my wife and enjoy a TV show. It sucks, but that's life, no parent I've spoken with differs in this regard.
> I have no idea how to spend my free time.
Another symptom of depression. Loss of interest in things we used to enjoy doing or withdrawing from hobbies. So what if you have 1000 games, they're there to give you joy not anxiety. You might have 9000 grains of rice in a 1lb bag in your cupboard but you don't worry about when you'll eat each individual one. Let them be, not playing them is as valid an option as playing them. Probably more so if you're time poor.
> Every time I'm asked to give an estimate for something I feel like I'm pulling a random number out of my ass.
I think software has this problem regardless, some of us are better at estimating some less so. I wouldn't worry about that. Unless you're repeating a development task you've done before many times (write a new rest controller, develop a CRUD web app) it's heard to give an estimate on something you haven't done before.
Pick a language you like and which advances the career you want and just start reading, hacking, messing around with it. Python's a great one for work and play tbh, but the important thing is to start. Most of the great coders I've worked with just get stuck into something new, they don't seem to care too much whether what they're learning will be obsolete or is non-optimal. I myself struggle with this one which is probably why I only know Java :)