Just need some advise...

So my husband has brought up a few times that he would like to have a three some (me him and another female) mainly to watch me in action with another girl. This obviously bothers me because I wouldn't want another woman touching my husband or him touching another woman and I feel like it's cheating, I don't know maybe it's just me and I'm over reacting but I can't stop thinking about it and it's bothering me. I have told him that I don't want to and don't like the idea, he respects that but sometimes it still gets brought up. Am I the only one that would be bothered about this?
Just need some advice...