Relationship advice?

Sometime during the summer of last year one of my friends and I both fell for the same mutual friend. All of our friendships were pretty tense for a while, as both if us liked the same guy and he liked us back. School started again and during late October I was talking to both of them and the guy brought up all three of us dating.

Obviously, myself and the other girl were a little bit cautious at first, as neither of us believed we were attracted to girls in any way. We decided to do a trial period for about a week.

After that week the girl and I decided that we were at least curious about taking our relationship farther, and both of us still liked the guy. Everything was going well until new years. The girl spent the night at my house (my parents thought we were both straight) and we cuddled and talked and stuff. But little things she would do kept annoying me. I figured I was just tired, and went to sleep without much more thought about it.

The next day we were making out and she went down on me. It felt nice, but I didn't orgasm.

Since then I've been hanging out with the guy more and we've been getting along great, but we haven't always invited the other girl to hang out with us. I've found that I enjoy myself more if its just me and him.

Tonight I hung out with the girl a little bit and things that she did were irritating me. How she talked and what she said and how much she touched me. All of it was irritating me.

I know she likes girls, but I don't think I do. I don't like her much either, even when we were friends she would irritate me.

The problem is, I still like the guy, and I don't really know how they feel about each other. We also have the same friends.

I know that I can't keep being with her if I don't like her. I just don't know how to tell her this, or what to tell the guy.

Any help would be greatly appreciated :)