My wife got me into anal sex with toys, Now she wants to see me with a man. I dont want that?

Me and My wife have been together for 1 year now 5 all together, One day she wanted to perform anal sex on me and I let her, Much to my surprise I liked it A LOT! She loves to do this and I love to receive it, I have my toys and I'm happy with that, But now she wants me to be with a guy while she watches, This I have a problem with and she is not listing to me when I tell her I don't want a guy I want Her, But she insist that I do this, Having a toy in me is one thing, I don't want any kind of anything with another man. The problem is that im a puss when It comes to a firm NO, I hem and haw and Im afraid ill give in and then well fight about it, How do I say NO I dont want it She says it will keep us closer but I see it pushing us apart, Am I wrong? What should I do?