Is it normal that i picture my boyfriend having sex with other women?

Lately, when I have been having sex with my boyfriend, I picture him having sex with other women to get off. I would never, ever want him to do that, and I am not a swinger nor would I ever consider becoming one but for some reason I fantasize about this and it gets me really excited in the moment, but then afterward I feel upset and shitty for thinking about it. Am I normal????