My girlfriend and male dog

I saw my girlfriend of six months being orally pleasured by her neutered male dog. She doesn’t know I saw her. I don’t know what to make of this. We both come from fairly conservative backgrounds and have limited sexual experience. I can’t imagine discussing this with her. But I can’t get the image out of my head. I really like this woman, and one side of me wants to say it’s no big deal, just another way to masturbate. But this is b********y, right? Isn’t it technically i*****l, or at least immoral? I keep wondering what she’s thinking while we have sex, and my appetite for oral is nil now. This is sad because we had been communicating well about sex (a first for me). I can’t talk about it with friends like I usually world. So I ask you, how weird is this? What would you do?