Well this happened kind of to me. I asked my husband for permission to open our marriage but I found i couldn't just "fool around" and I ended up just telling the truth. A lot of things have happened since then but my husband and I are still together. I don't know if I hurt him or not but he seems to be ok with what I am and what I do.
I don't know how to approach it in your situation, as you have to be careful and it sounds like you are trying to have consideration for everyone. Good luck whatever decision you make.