And [being] on the spot I replied, ~

The protagonist, the one of Amber's princes with amnesia talks one of his sisters. Here, he tries to seems normal.

And I felt uncomfortable.
My anger was there, and I wandered whether she knew who it was that I needed to stay it. I felt that she did. I fought with the desire to ask it outright, suppressed it.
"Well, what do you propose doing?" she finally asked, and being on the spot I replied, "Of course, you don't trust me. . . ."
"How could we?"
I determined to remember that we."
<Nine Princes in Amber" of The Great Book of Amber by Roger Zelazny>
I'd like to know why there "being" is in "being on the spot I replied."
Thank you in advance for your help.