Back story is I've been seeing my BF for about 9/10 months. We work together. There is a girl (we'll call her Sarah) that we work with that we're both friendly with, but I get a little bit jealous of how they are sometimes (he says irrational and to be fair he might be right). Anyway I got to work, already stressed and grumpy and first thing I saw was them together so got a bit annoyed and he could tell. (stupid i know)
So in the evening we are having sex, and he says something along the lines of "does sarah turn me on?" so I'm a bit shocked 
and so I say "no" (bloody hope not). And he says a couple of other similar things.
I said to him after it was a massive turn off from him to bring her up while we're having sex, as in my eyes it just made me think "we're having sex and you're thinking about her". He didn't really understand why it upset, said that he was trying to get me to see it's me that he's with and that he wants. Apologised for upsetting me but I could see he didn't really get what the problem was?
Am I being unreasonable to be upset that he did that?