Is it normal that I feel like I can be a bitch to my partner?

You might try making a conscious effort to actually think about what you're about to say before the words come out of your mouth. I'm convinced that a lot of people never do that. They spout the most hurtful, unfair, untrue stuff without thinking about it beforehand. The worst sort are those who then never apologise or explain afterwards because their delicate ego just won't let them accept that they've screwed up.