Not sure if breaking up was the best idea anymore

Hi everyone, I am here cause honestly I didn't know where else to go right now to discuss these things. I feel like i might have messed up a lot of my close relationships and friendships in the past couple of months.

So let me start from the beginning.

I was in a perfectly good relationship. My boyfriend (Lets call him Mike) and I were together for about 4 years now and things were perfect, i think we were in mad love. My mother knew about this and was supportive too. Nobody in his family knew but eventually we would tell them. Then we both had to move to a different city. This is when things got out of hand. I haven't had a very good experience in a long distance relationship before (the guy cheated on me) so I wasn't sure about this one. Mike in general too wasnt very good at keeping in touch when away. But we said we will give this our best shot. For a couple of months things were changing in both our lives. We were meeting new people, making new friends, we had new jobs. It was kind of hard to keep each other updated about the things that happened in the day/week. We were busy and couldnt find time to talk. What's worse is he stays at home and hadnt told his parents about me. We still got through it, fought and made up. He visited me a couple of times, I went over to visit him. I thought things were going well finally. We still wouldn't be able to really talk and connect, but it was okay. But soon enough, we fell right back into the hole. The only messages we exchanged in the day was a good morning and goodnight. Barely 2-3 phone calls a week. We had stopped connecting, atleast from my end. I didn't find telling him what happened in my day exciting anymore. I didn't think of him when I saw other couples. There were days when I would just cry realising that I might be falling out of love. I didn't want to. I really really didn't want to. But it was happening.

Here's the tricky part, there's a back story. During this time I was getting close to another friend/colleague of mine (we'll call him Jack). Now Jack and his then girlfriend (say Nina) and Mike and I, the four of us were a part of the same group of friends back when we were together in the first city. Infact Nina and I were closer and better friends than Jack and I were back then.

Jack broke up with Nina about the same time that we moved to a new city for a new job we got together. Since then we started getting to know each other better. We got close (just as friends). He would flirt occasionally but it was healthy flirting and he knew I was in a relationship with Mike. Mike and Jack were friends too (as i mentioned before). All was good until I started having issues in my relationship. Soon I started having a slight crush on Jack. Jack and I are great as friends. We do crazy fun stuff when we are together, but we are very different and I know that if we were to get together, it would not last. Yet i had started having feelings for him. Maybe it was the fact that it was convenient. Having him work at the same place, being in the same group of friends, being able to see him everyday. Maybe I really wanted these things from a boyfriend. Maybe LDR wasn't working for me. There were so many mixed feelings.

Mike and I spoke even lesser now. My feelings for him started vanishing. Many-a-times I had come to the brink of breaking up. We took a gazillion breaks. We fought and discussed our relationship and why it wasn't working. There were other issues we had too which we couldn't solve together. The twig really broke when I spoke to my dad about it and he didnt seem approving of this relationship. Now call me a coward but I really can't stand upsetting my dad. With my feelings dissolving, having constant issues in the relationship and my dad's unapproval, I decided I want to break up once and for all. And so I did.

For a couple of weeks, it was hard. I would think about all the things that I could have done better. All the happiness we could have found. I would cry and I would miss him. But when he called for the same, I would be so cold to him. I thought it'll help him get over me faster. Jack and I started getting closer during this time. He would come over to cheer me up. Sleep over too sometimes. But nothing ever happened between us. Jack had done this before too when I was in a relationship and it was okay. Nothing seemed like a sign. But now when I had broken up, everything seemed like a sign.

I couldn't take it anymore and discussed this with Jack, I told him what i'm feeling. I told him I miss Mike but somehow I had feelings for him(Jack) too. I told him it's a phase and it will pass. I asked him about the things he had started doing for me lately. He explained to me that it was purely out of friendship and nothing more. We both understood this and agreed to move on without any awkwardness.
But then came Jacks birthday, and in an unforeseen turn of events with a big push of alcohol, I had to sleep next to Jack on a small bed. We are both unsure but we found ourselves wrapped in each others arms in the morning. Nothing had happened. We had just hugged and slept. This was a bit awkward for me but I let it slide. Since then whenever he would come over or I would stay over at his place, we would always hug and sleep, no questions asked. We never spoke about it and somehow it was just understood. And then there was another night (this was almost 2 months after my breakup with Mike). Jack was staying over and we were both quite drunk. With our inhibitions lowered, we found our faces too close to each others. Before I knew it we had kissed and made out a little. Somehow it felt very normal. It felt like I had been doing this for ages. As soon as it hit me what I was doing, I freaked out. I got up and started panicking. I calmed down after a while and realised that I cannot undo this now, so why not continue. Maybe somewhere deep inside I wanted to do thing that I might regret. For quite a while, about 3-4 years my life had been a perfect constant. I think I wanted to stir it up.
Since that night, Jack and I have been meeting up, being sexually involved. But the feelings I had for him are gone now and he doesnt feel anything for me either. Its hollow. And I feel like shit after it. But we still continue.

Sometimes I cry and I dont know the reason for it. I cant sleep for hours at night. This is taking a toll on my body. I break down in front of people even if there was no trigger. I am not happy.

I am confused why I am doing this. I am sad that nobody will understand me. I have ruined any chances of me getting back together with Mike. I feel like I am cheating on Nina somewhere deep down. I fear I have spoiled my friendship with Jack forever. Im stuck in the middle somewhere now and I feel like a cheater, but I cant stop.
I dont understand what I am searching for.