[Ianto is thinking along the same lines even if he hates himself for it. He's not afraid for his own safety; Spike has proven more than once how good he is at controlling himself around him and he has to think that counts for something. Jack's death doesn't really help his theory but he knows how overwhelming Spike finds him, and no matter how much they care about each other they aren't as close as he and Spike are. He has to believe that those feelings count for something in the face of all this because otherwise what's the point of any of it? But unfortunately he finds it all too easy to believe that if something is making him lose control no one else here is safe. He's not scared of him but he is scared for him and what this will do to him.
There doesn't seem to be much point in saying any of that though, not when he's sure Spike is thinking the same thing.] Do you feel up to looking for Jack? He might be able to help us get some answers.