If it's any consolation, I'm in my 40s and I have 3 kids and I honestly have days where my burnout and anxiety is as bad as you describe. I don't think it's not having kids that is your problem, I think you're probably predisposed to having an anxiety disorder and you're going through your mid-life crisis.
Note that I'm not downplaying the seriousness of your situation by calling it a mid-life crisis - the mid-life crisis is real as fuck and it's a force to be reckoned with. I think the trick of it is to redirect that angst and energy into something useful. Rather than wreck your marriage and run off with 27 year old, maybe you should try an entirely new career, or get into volunteer work, or take a 6 month sabbatical. Who knows? In any case, be very careful of what bridges you burn. I'll let you know if I figure it out...
Can vouch for post-40 mental weirdness that is probably the midlife-crisis instigator. My brother in-law, who's a couple of years older than me, went through something similar a few years ago that nearly cost him his marriage.
To some extent, my brother in-law's experience helped me get through mine because I was able to join the dots and identify my mental bullshit as coming from the same place as his, and try to avoid making the same mistakes.
Note that I'm not downplaying the seriousness of your situation by calling it a mid-life crisis - the mid-life crisis is real as fuck and it's a force to be reckoned with. I think the trick of it is to redirect that angst and energy into something useful. Rather than wreck your marriage and run off with 27 year old, maybe you should try an entirely new career, or get into volunteer work, or take a 6 month sabbatical. Who knows? In any case, be very careful of what bridges you burn. I'll let you know if I figure it out...