I Am Unsure About My Sexuality

So I'm a bisexual woman. Maybe. It's what I've called myself for the past two years. But lately, I've started seeing a guy. He's incredibly nice and sweet and just treats me so well. Compliments, positive feedback, such a great person. But I'm starting to feel less attracted to him. My whole life I think I've found girls more attractive...most men I've found attractive tend to be more feminine in appearance. i mean, it's not like I find guys repellant. But I'm confused and I don't want to be. I don't want to give bisexuality a bad name, since so many people call bisexuals confused. I feel guilty for not being certain. And I'm afraid of hurting this wonderful guy...maybe I should just give him some more time? Maybe I'm just not used to dating in general, and regardless of gender I'd be just as iffy? God I wish I knew. I wish it were as black and white as a lot of people seem to think it is...