Question for bisexuals: Dating the sex you DON'T prefer

I'm still learning a lot about bisexuality. My boyfriend is bisexual. So I've learned that not all bisexuals like both sexes 5050. Some have a preference. My bestie prefers guys. Well my boyfriend prefers man. And it does kind of make me feel insecure, but that's a me problem Ik. My bestie is in a long1 term relationship with a girl even though she prefers men so ik it can work. I guess I just want to understand what exactly a preference means and does that mean you'll love the person less if that's not the sex you prefer? My boyfriend said he personally felt like dating men was just easier and that a lot of the women he dated expected him to read their mind where as when he dates men they just say whatever they feel. I'm the type who says whatever is on my mind. I just want to understand bisexuality more.