Hey, Three Olives, and welcome! I think it's generally accepted by many professionals that homosexuality/heterosexuality is not really just an either/or matter. Rather, people can be rated on a continuium (sp), with completely homo on one end and completely hetero on the other. It could be that you are falling somewhat in the middle.

Are you happy with your husband? Are your sexual needs met satisfactorially? If you are not having regular sex with him and/or are spending a lot of time with this woman, then this tendency might show up.

I don't know that it particularly has anything to do with your being in your forties. (Not a mid-life crisis thing, I don't think, anyway.)

My opinion is it would be best not to tell either one of them. Of course, if you find out for sure that she can swing in the homo direction, and you really want to check this out, then that might be another matter. However, be very sure, because you would likely lose your marriage if you choose to experiment and your husband finds out.

You might need to find some way to not spend so much time with this woman, if it's really driving you around the bend. Seeing a therapist might also be helpful for you, IMHO.