Wondering Mom

This happened about a month ago. It was in the middle of the afternoon and my husband and I decided that we felt like having sex.
So there we were, naked, with him on top of me, and we were doing it. It was quite nice and we were enjoying it. Then suddenly I was surprised to look up and see our eighteen year old son standing in the door way. He had obviously come back home much earlier than we were expecting and we had carelessly not closed the bedroom door all the way.
He had this surprised and amused grin on his face. I didn’t know what to do, so I just smiled back. His father became aware that he was there, and grinned. And we just kept doing it. Our son left after a moment. When my husband and I finished we both were a bit modest about this as expected, but we laughed, and my husband joked how maybe we should invited him to join us.
Later we all had these modest grins, but it had just been one of those things and no harm was done. Then I started thinking about what my husband had said about having our son join in, and I was surprised that I actually began to find this to be a not unappealing idea. I couldn’t believe this, but I found the thought of doing it with both my husband and son at the same time very exciting and sort of wonderful.
I did later jokingly remark on this with my husband and he said that it would be fine with him. Now I’m really wondering if I should go through with it.
I will write more later if I decide.