Wondering What To Do

I am a forty-four year old divorced mo. For the last four months I have been having a bisexual affair with my eight year old son’s girlfriend. They have been seeing each other for almost a year, and she and I have always gotten along. In fact, there seemed to be a very good female chemistry between the two of us. It all got started when one day it was just her and I and we were talking and, I don’t know, it just seemed like we both wanted it to be more. We kissed, quite romantically, and it just went from there. It took very little effort for us to find ourselves naked in bed having some the most wonderful sex.
Like I said, this has gone on for four months now, and we have both tried to stop but with no success. My son has no idea of course, and both of us could imagine what he way say if he found out. I know that I would be terribly embarrassed if he did. I had never done anything like this before, and she admitted that she has a few bisexual momnst with a friend, but that is all.
I am twice her age and we both realize that there is no future for us so far as trying to become a couple, but no matter what we are finding ourselves becoming serious lesbian lovers. Does anyone have any advice?