Lesbian in love with a man

I am a lesbian. I've only ever been with women. I've never been with a man in any sense. I never have felt inclined toward men at all. But I fell in love with one. Or I thought I did. We haven't slept together and I'm scared that I might not want to. He turns me on. I'm sexually attracted to him, but the actual act freaks me out. And yesterday I started feeling less romantic toward him. We hang out and are affectionate with each other all the time. He knows where I stand about sex. But I'm worried it's not just a mental block. I've felt enamored up until yesterday. I don't want to throw this away, but do I have to? Is by sexual preference really that extreme? I love him deeply. But maybe I'm not in love. I don't know. I need to find someone who's experienced this and I can't.