I think the issue I see the most in the bisexual community is "Am I straight? Or, am I gay? Where do I fit in the continuum of sexuality??"
It's good to evaluate what you feel and why you feel it. But in the end sometimes for some things feelings are feelings. They happen. You don't control them all.
I'm reluctant to assign negative terms like "sexist" to how you feel about relationships because it can be such a deep thing you may never change, or if you do change it may be a long time. And there's nothing wrong with straight relationships in the first place.
As a bisexual person you may have to come to terms with both sides of your nature and be just as ok with the straight side as the gay side. Don't be hard on yourself or shame yourself into new ways of thinking. Where you are today is ok. And if where you are tomorrow is different, that's ok too. It doesn't have to be a "right" or "wrong" thing at all because there's room in this world for it all. :)