54 here. I'd have told my 40 year old self to LTB and to believe in my ability to cope on my own.
Other advice would be:
Try really hard not to catastrophise and think about worst case scenarios - the situation that ended my marriage and resulted in me having to rebuild my life completely with the princely sum of £750 to my name, was not one I would have even thought to worry about.
Whatever happens you will get through it. You don't know how strong you are until the only choice you have is to be strong.
Eat as healthily as possible, drink in moderation, exercise and invest yourself in friends you have and in making new ones. As you get older and children leave home and parents and other relatives die, you will benefit so much from having good friends around who support each other as well as having fun. If you have tried as hard as possible to maintain your body, you'll be able to do more. The saying "Use it or lose it" becomes more and more important as you get older.
Have fun - try not to take life too seriously. Keep things in perspective. The more things I've been through, the more I let everyday annoyances wash over me. I've experienced the serious illness and deaths of my parents, an ex who defrauded me, the divorce from hell, homelessness and being a witness for the prosecution against my ex. So if I get a stain on the carpet, or I prang the car, my computer plays up or I break a much loved ornament - it bothers me very little.
Be grateful for what you have and don't look to possessions and the acquisition of more possessions, to fill any holes in your life. They can't and won't.
If you are in a marriage that really isn't happy and with little hope of improvement, try and find the courage to end it. I look back and feel so bloody angry with myself for wasting so many many years with an irresponsible twat because I didn't believe in myself enough to get out.
Say yes to new experiences for both yourself and your family. Trying something new, no matter how small, keeps your mind alive and enquiring.