It's trite, but it's true. My main suggestion would be to get out there, to be active. Join Meetup groups or other social groups, find others that share your interests. Do volunteer work. Especially if you live in or near a large city, the opportunities are endless. Staying at home, alone, I think is the worst thing you can do.

You could look into a part-time job - I know people that are close to 70 or over 70, that work part-time, and it helps a lot not only with their financial situation, but with loneliness.

About being pre-diabetic, you should read about Ray Kurzweil's experience in curing his condition by changing his diet - there's a lot that's been published since then on it.

Many are in the same boat in terms of not having an LGF (including myself) - I think it's important to not rely on external things for happiness, otherwise your own happiness will always be subject to the vicissitudes of fate.

A reason to live: you have to make one for yourself. I don't believe that there is any pre-determined reason for anyone. But that gives us the freedom to choose our own reason for living, and allows us to own our own life.

Come meet me in chat if you want to talk sometime.