It sucks to see golf buddies leave. I was military so have seen my fair share of friends come and go. The bright side of it all is that I have golf friends all around the country now. I feel like a lot of what you are going through is more common that you think in the 40's. I started losing the distance after 35. It really hit at 40.
A few thoughts come to mind when reading your post. If you have never had a fitting, do it. Make sure you are in the right gear and have zero question about it. Take care of the back as best you can. Try to do some planks and body weight PT drills to help keep your back in some decent shape. I know it is tough to come back from though in my own experience. Also, check all the fundamentals. Make sure the grip is good and your set up for the shot is proper. Small changes in the set up and grip can easily create some issues. Finally, if you are really struggling with getting the weight forward, you could try a pressure plate board to help get a feel for it. Focus on pushing off that lead leg to clear the lead hip should get you going in the right direction.