Over sensitive?

It's 07.12am. Boyf. has left for work and I feel a little bit sick. I told boyf. that I dreamt last night I found him with another women. (The dream came from a comment about his ex coming back I think). This in itself was bad enough, he then says to me 'thats really weird, I dreamt I was with another women last night too' he then proceeded to tell me it was ok though it was just a sex thing and she was a really fit mexican looking women, purely lust. I am actually shocked at how upset I felt at hearing this - even writing about it now makes me feel sick. It's odd because even though he hasn't actually done anything, it's like we are lying in bed with one another and he is dreaming of being with another women. Should I feel this way? I know even when we are in relationships we can dream of being with other people, and it doesn't mean anything, but I am thinking now we should definitely keep it to ourselves. I actually shed a tear which of course I didn't let boyf. see as was a bit embarrassed. It does actually scare me a bit as I love Boyf. so much and that is why I got upset, I could also say it's my own insecurity and maybe I don't feel secure in our relationship. I think it's just because I found the conversation quite horrible.