This situation is both confusing and upsetting. I just don't know how to proceed in regards to my sister "Jen"

I guess I should start at the beginning, which I have been told is a good place to start, go figure..

A quick background blurb abut me. I am the youngest out of 3 (counting me) siblings who i GREW up with on my mothers side. My sister and brother have a different father than I but we all lived with our mother and stepdad...

My Father left my Mom (or Mom left him) two years after I was born and we moved pretty far away so I did not have any type of relationship what so ever with my dad at all. When I got around the age of 10, I started asking questions about my dad (it was a crazy insane relationship between mom and dad, but I never knew till YEARS later how bad it was..Mom never told me and never said anything bad about him-she wanted me to make up my own mind about him...)
So mom tracked him down and they decided that in the summer I would go and meet him and stay with him for a few weeks. The summer came and I stayed with my father and his family (wife and HER two sons from an early relationship) while I was there dad told me about a son and a daughter he also has that he has lost track of, a son who is older than me by 3 years and a daughter who is 5 years younger than I. The daughter was from a quick relationship and the son was from a women he dated before he met my mom. The son lived somewhere in California and my sister lived in Michigan the last time he knew. He did not pay child support to any of his children except for me.

My step mom and I did not get along later in life and the last time I talked to my dad i was 13. 12-13 years later my sister tracks my father down and reconnects with his side of the the family. His sister(My Aunt Tammy) who I am still in contact with got in touch with us(mom and I) telling me that she wanted to meet me (we still have never meet my half brother to this day)
We started to chat with each other via Phone and IM and we instantly "clicked" and had so much in common. We were both part of the same type of extreme music scene had the same taste in movies and dressed alike (crusty punk scene) held the same political beliefs and we are both HARDLINE Atheist's.... so on and so on, just trying to fill each other in on our lives as fast as we could, I guess trying to make up for the years we were apart. She was happy to be a sister since she was raised as an only child and before she started to talk to me, she tried to find our other sibling to no avail....anyway...

We would stay up talking to each other for hours and laugh at each others stupid jokes and we seemed to understand what each other was thinking, we just really connected. when she found out that she got accepted to the State University I lived by (I am a 20 minute WALK from campus)
we were both very happy.

After she moved into town we started to hang out all the time, and became very close and affectionate to each other, even sleeping in the same bed when she stayed over. This went on for about a year, doing everything together, calling each other up when one of us had a bad day, we really relied on each others love and compassion, it was nice and it felt great. One night we were cuddling on the couch watching a movie while she had me "tickling" her back (lightly move one or two fingers around her mid/lower back, its NON-SEXUAL trust me...)
As we laid there talking, like we have done a million times before somehow, out of the blue, we were making out. I stopped and just froze. All of these feelings hit me at the same time, I was shaking because my body responded like it should be when you're kissing someone you're very attracted to for the first time, but I was also filled with such guilt and repulsion but something else was pulling me towards her. All I could think of was her, how I wanted to be with her in every way a human can be with another person.

I was horrified at how I felt. I just sat there speechless, and Jen just started opening up and told me about how she had feelings for me and how she has never connected like this with any other guy and never felt so intense about another person, it felt like she was going a million miles a minute. I felt the same way but I blocked it all out for so long that when it did bubble up to the surface it was too much for me to handle, facing the truth anyway and now her she was telling me the exact same way of how I feel...It was too much and I felt sick.
I couldn't tell her that I felt the same way, I was afraid that doing so would only make maters worse. The thing is I have been feeling like this towards her for awhile now, it's like this heavy dark force has come over me and all I could think of is her and the attraction is very intense but I refused to think about it like that, so I buried it to the point of self deception because I figured it was a one way feeling and that it is completely wrong to even feel this way.

Anyway after she poured her heart out to me, I felt that there is no way I should tell her the truth about my feelings and how I am going thru the exact same thing because doing this would have only made things worse and it would have given us both a validation and it very well could have crossed the line. It was bad enough how far we got when we were making out on the couch, doing things that I should not have allowed to go as far as it did.

I ended up leaving her place and walked home, feeling so many emotions wrapped up in a ball of confusion and guilt. I knew I had feelings for her, and I truly desired her in ways I have never felt before, but because of feelings this way I would be filled with guilt and shame.

I hid in my Apt for a few days afterwards with jen calling me and texting me and me feeling too guilty and shameful to answer. It got to the point that she had to come over just to get me to talk with her.
I told her that I was too confused and that we shouldn't hang out with each other anymore(When she came over and I saw her, I was filled with a weird excitement along with this intense desire to be intimate with her, I felt that it was better off that I kept those feelings to myself) or we would regret it and that what we are doing is wrong. She cried and i felt my heart break but I just could not trust myself. The desire and the attraction stronger than anything I have ever felt with before and I know that if this went on unchecked we would cross a line that we both could not come back from.

I ended up blocking her from social media while telling her that it's not her fault and that I will always love her, I don't want her to think she freaked me out and I am disgusted with her, tho this is how she feels because she does not understand why I felt the need to just cut her off.
I want her in my life but we both act like we are madly in love with each other, tho she does not know how I feel towards her (she prolly has some inkling because of what went down between us that night) and I do not want to act out these urges because this is what is bound to happen. I cannot explain how intense these feelings are, but trust me when I tell you that I am afraid of giving in, it feels like I am powerless. She is all I can think about and when ever we do talk, she tells me the same and the more she tells me, the more I feel like I need to be with her.
Anyway I told her I nneeded my space and she has granted me that but I had to block her from FB because she kept PM me trying to get me to talk to her before that...
It feels like I lost my best friend and I miss HER SO MUCH, but yet I am obsessed with her and have had sexual dreams which makes me feel even worse with shame...

I just don't know what I should do at this point. I dare not TELL ANYONE what I am going through but I also know that I cannot keep myself away from her much longer, I miss her deeply and I do crave her companionship so much I'm just afraid of things going too far..
Should I tell her I feel the same way and hope that we can talk thru it and come to an understanding? I don't want her to think she messed up or that I feel disgusted with her or that it's all her fault (things she has said to me before) amd that's why I cut her off. Should I be honest at least?

I know this is prolly going to make a few people disgusted and I understand that, but please try to keep those comments to yourself and try to understand and put yourself in my shoes..

I am very confused and I know she is suffering as well...am I being selfish?

I don't know what to do....