Some people never fully understand their sexuality. It's not exactly an easy subject - there are many subsets, many contributing factors, individual biology and personal experience to take into account.

The best way to at least attempt to work things out, is to actually try them. If you feel you'd like to act upon your fantasies then do so - who are you hurting? You're at the time of life when you've worked hard, you've already dealt with the expectations of others for a long time. Now should be about doing what you want. You're never too old to at least try. Figure out more closely what it is you'd prefer e.g sexual encounters or a relationship and then maybe look online for the right way to put yourself out there. There might be a lesbian/bi/curious meet up sight for 50+ women. What about online support groups? There must be something out there for ladies of a certain age that are still coming to terms with sexuality etc. Previous generations have found it more difficult to express this sort of thing - acceptance has only started to gain pace in more recent years. So the fears you have are totally understandable but there are outlets - it's merely a case of finding them.

Perhaps you could seek professional input if this is something particularly concerning for you? I'm sorry if my suggestions have not been too helpful - i hope other posters have something to contribute to your thread. All the best.