[larkinnaire]

You're not alone -- a lot of this resonates with me, but I (also in my 40s) might be a little further along in my journey and have a few more resources to draw on. But I feel this.

The most important thing: therapy. Don't spend too much time finding a therapist -- take the first one with an opening. If you don't get along with them, ask for a referral or use a method discussed in other comments. But the important thing is to start. Many therapists will do video calls now. Medication can also be effective.

Some more good stuff about your life: * You're not too old for marriage or even kids. Guys are lucky in that respect -- we have an easier time finding partners and having kids when we're older. * You took an important step: you posted this question. I am terrified to do any such thing about my own problems, so I respect you a lot for it. * You had a network before, and professional networks are more resilient than you think. If a co-worker from 10 years ago emailed me out of the blue, I'd be happy to talk to them. I think you'd be happy to talk to your old colleagues, so why the assumption that they wouldn't respond to you? That's an example of catastrophizing thinking. A therapist can help you with that better than HN randos...but still, asking HN randos is a good step to take! * It's not a given that the best of your life is behind you. Every part of your life can be the prime of your life if you value the things that part of your life has to offer.

Good luck, friend.