It happens to everyone sooner or later. We all grow old. We begin to loose our faculties and need some kind of assistance. Most people used to think that their children would be there for them and years ago they were. Those were the days of the extended family. Now this is not so true any more.
Whether gay or lesbian, you will need to plan for your old age without expecting any assistance from anyone. This may not extend to your spouse but it generally extends to mostly everyone else. That means that you need to plan to have a good savings plan and investments for the future when you are no longer able to earn a living. Of course, this is true of straight people as well.
There are other issues as well. These involve a kind of nurturing that we humans need that we know as care and compassion. Many straight people think that this will come naturally from their children but some are bitterly disappointed. I could quote the "bread cast upon the waters" thing but you know by now that the love that you share and give away has a remarkable way of coming back to you.
Be a good and loving and compassionate person. This takes a lot of work. It means going to see the sick and dying now. It means taking an interest in the needs of others now. It means supporting our own charities. Aids, Women's issues, etc. You will be surprised how much joy you will have in your life if you spend it thinking of others. You will just not have time to dwell on your own problems.
When you are unable to go out and give as you have in the past, you will still be able to answer the phone or fold papers for circulars. There will always be something for you to do.
And when the time comes, and you are ready to breathe your last, you will just be moved to another level somewhere out there where you and I will be free at last.