Betrayed Sister with her Husband

When I was 13 my sister brought a man home for christmas to meet the parents. I was having the classical unhappy childhood of violence, silbing fights, changing schools with no friends and suffering in my own little world. I clicked with him right away and it was like he was the first person who ever talked to me and asked about me and cared.
That developed into friendship and when I was 15 and my mother didnt know what to do with me anymore she agreed to let me go live with my sister and her then, husband....in a foreign country.
I sort of finished high school online, he gave me a job and for the 4 years that followed I was mainly living with them, or close to them and became very close to him. We had a lot in common that my sister and I never really did.
When I was 19 and after their second child, she went home for the holidays, and I stayed to finish up a work project with him. He started hitting on me out of the blue, never happened before nor did I ever think he saw me that way, nor did I have any attraction to him.
Taken off gaurd, at first I thought he had started using drugs again, since he was a 10 year clean recovering addict. But as my best and only friend and only person I had really ever connected to in my life, I had this huge emotional attachment to him, and trusted him. I didnt stop him. Not trying to defend myself, just saying thats my reasoning. And then,
it started to feel good.
It then progressed to outings, to touching, to vacations and to sex. He was my first.
And then to made up workprojects while we traveled together, to me saying I lived in cities I did not live in while actually living with him in the same city,(he would go home for a while each night, and she just thought he worked insesantly, which was always true before me.
It progressed to me falling in love with him, to us contantsly fighting and crying over how to make things right, because if we spoke up he would lose his kids, and I my family.
It progresed to me getting 2 abortions, while my sister was simultaneously having children.
To me listening to her marraige problems, the fact that he would never touch her anymore, and me not saying anything.
I tried to leave, and atleast 4 times did leave the country. But not only was I madly in love with him, he was my only friend, the only one who I could talk to about myself since my whole life was a lie, he supported me basically, gave me a job since I had no education, supplied my work visa to stay in the country, and the list goes on. I always came running back, not knowing how to be without him. Or he would come get me and we would be inseperable.
Our relationship got worse and worse, and I started to get sick, physically and depressed, with all the lies, betrayal and knowing that this had to end. Until I actually developed a heart condition and started having panick attacks, almost every night, for 3 months straight. I could not be alone, and it was just this huge wake up call that I had to break free now, or this is going to kill me. Literally.
I packed my bags for the billionth time and left at age 27. AFTER 10 YEARS.
I rarely spoke to my sister anymore, because of the guilt and seeing her before I left she once again poured out all her heart break over this man who is madly in love with (her husband) who does not know how to be with her, who does not touch her, that she just cant save their marraige. and she was packing her stuff and leaving him.She is now living with her kids back at our moms house, and I am living in an apartment on the tip of a random country looking for work, and trying to figure out how to deal with life.
I couldnt say anything to her when we parted .I just cried with her, and wished so hard I could take her pain away, knowing full well I was behind this all.
I feel like I have done something so horrible that there is just no way to make this better EVER. The betrayal to my sister, year after year,. I feel like I don't deserve anything good, ever, and that I should only hope for the same in return. I selfishly keep what Ive done to myself, because I dont want to loose her. and our relationship is a lie, I dont deserve her love.
But even if I did speak up, now i feel like the hurt would only be 10 times worse, and it would only be for my own personal satifaction to try and take the guilt off my shoulders or something. Because she would be hurt for life, by what Ive done and what he's done, it will affect his relationship with his kids, their relationship with me, my family will be hurt etc.
But at the same time, I feel like keeping my mouth shut and just moving on......why would I ever deserve to forgive myself , if I cant ask for forgiveness. if i cant say that I fucked up. really really fucked up.
And why would it ever even be worth while to fight for something better, when I cant wrap my head around why I would deserve anything but lies, and betrayal right back at me. How could I ever deserve any sort of healthy relationship or good life. How could I ever make up what I have done to her.
I feel like a worthless piece of ****, and any way I look at it, I dont see any way to even mildy fix anything.
I still love him, but Im not going back this time, our relationship, my life, his life, and the life of everybody around me I feel like is broken into a million pieces, and what I want more than anything is to not loose my family.
When i was 19 and stupid I used to dream of disapearing in China, with him, now I dream of standing by my sisters side, of making things right with her, of being a good aunt, of being there, and being close to my family, but Ive betrayed something that runs so deep, and for so long, that at 27 I can no longer say Im just stupid, I am stupid, but I know better... There is just no way to make this better. What do I do? I have only told this story of my life to one person ever. My therapist. He told me Its not as bad as it seems, and that I need to be able to talk about this with people in order to have relationships and be able to share my life. I said I cant do that, I would never want to relate to me, if I was somebody else. He said what if you post it somewhere, and just see, that people will be more sympathetic that you think. So here it is, im posting this, so you can tell me how fucked up I am, judge me, say whatever you really think.Just give it to me straight. I need to hear it.
I do not believe as he states, that i am the victim of my own reality having been seduced by an older man at a young age, because this goes so above and beyond that. this is killing me inside. Where do we go from here?