What do I do in this situation!?

Okay let me start from the beginning. I recently moved from my hometown of Coos Bay to a small town in central Oregon. I am now in a new school, I met a very beautiful girl there! I mean stunning. I'm kinda a shy guy so I never really talked to her or anybody because she is WAY "out of my league" She is a track star, 4.0 student, and leader of volleyball. I am just a shy new kid that has low self-esteem. I made a few friends and on December 19 I was invited to my friend Katie's birthday party. I went and that girl was there with her boyfriend.

Now I know girls think I'm not that bad looking because I care about my features. But I just don't like them. Well the girl was there and that night we were all in the bed of Katie's truck talking. I learned this girls name is Mariah. She was playing with my calves and feeling my muscle of my legs and just kinda being touchy. I was worried her boyfriend would see, he did, and he didn't care though. I got her number and we got to know each other extremely well over the last 3 months.

Her boyfriend and she broke up and I was there for her. That's when we first kissed. She told me that I am the most caring guy she has ever met and she loved me. I'm not going to lie I felt the same way. In those three months we spent almost 400 hours on the phone together alone! So we had a pretty strong friendship. A little about me, I am a shy, blonde 15 (16 in one week) year old. I am a published author and want to be a computer network engineer. I have only kissed Mariah and one other girl in my life. I am proud to say that. I am also a 4.0 student. Okay back to the story. Mariah was guilted back with her ex (Taylor) because he said he made a mistake dumping her and he was going to kill himself if he couldn't be back in her life. (Stupid I know, I hate drama! I try to stay out of it.) Well they got back together and he found out we had that time together and that we kissed. He was enraged! He threatened to fight me and even assault me. Now I may be shy but I am strong and I could easily over power him in any fight.

Fast forward to about two weeks ago, I have tried staying out of their lives and whatnot but I guess I hugged Mariah wrongly and Taylor flipped. He started insulting my Family and I DO NOT tolerate that. I was going to hurt him. Bad. I calmed down and thought what the consequences would be if I did hurt him, I decided it wasn't the smart thing to do. I stuck to my motto "Kill them with kindness" and apologized. I forgot to mention she moved 4 houses down from me January 12 (I don't know why I remembered the date) She still tells me she loves me and I say I love her too. When we say it isn't meant to hurt anyone and Taylor knows she loves me, but he doesn't do anything about it. (Kind of weird) 3 days ago she came to my house so I could help her write a poem.

My father called and invited her to go to see an organist with us. She agreed and went. In the car she held my hand. (Kind of questionable) At the concert she put my hands on her upper thighs. (A little more questionable) We went out to eat and on the car ride home she started falling asleep on me. I let it happen and she looked up at me and leaned in to kiss me. I shook my head no and told her she has a boyfriend. We had to run by my house to get her keys. I was in my room when she picked them up from my desk, she leaned over and our lips met. I kissed her three times. I walked her home and that was the end of it.

Wednesday. School was fine, but the bus ride she said she wanted some help with homework. She came over and we studied for about 40 minutes. Before I knew it we were making out on my bed and she was grinding her body on my abs. When she had to go home she made the comment "this is so cheating" and smiled. This IS NOT her. She has never cheated on a guy and said she could never think about doing that. Thursday, same thing happened. Today is Friday and I can't stop thinking about her. I feel guilty. I know it's wrong, but I love her. I'm confused. If she wants me why is she still with Taylor? Why is she cheating on him? I feel like a bad person, and this isn't me! What do I do?!