I'm 40 years old and have no friends and, outside my wife and kids, no family that speak to me. There's never been any specific fall out, we're just not really in contact. I've been to college, university, had 6 jobs at big companies in sales / management positions and am in touch with nobody from any of these thousands of interactions over the years. I tried social media a few years ago to reconnect with people I used to know but nothing came from that - I even joined a chat site for lonely people once and ironically nobody spoke to me, which was kinda funny at the time. Not that it should make a difference but I earn relatively good money, live is a niceish house and run my own business. I get involved with events to help animal charities, play guitar, read a lot and am well travelled so I don't get why such a wide range of people that I've interacted with don't like me. I go to the gym every day and watch the instructors walking around chatting to everyone with tips and technique advice but I even get bypassed with that, and these people haven't even had chance to judge me yet! So what to do, thinking about the future when my kids are gone there seems very little purpose in a further 30/40 years of solitude. And not that I'm suicidal, but it's sad to think that if I was suddenly removed from the world it would take a very long time for anybody to notice and nobody would be particularly bothered anyway...
I'm baffled really as you have a wife and kids and I assume they will all be around for a while longer and surely, if you are a good Dad, your kids will always be there for you ? You say you do stuff for animal charities, so you are obviously an animal lover. At a low time in my life some years ago, I took up dog walking at my local RSPCA, this could be a way to make new friends.
If your children are school age try offering to help out there, with your experience your help may be invaluable and you'll meet others of a similar age and situation too.