Novel sized problem...really need help tho

k this is a bit of a long story...so here goes:

I'm in grade 12 dating a girl on and off since grade 10, and like her through grade 9 and 8.During grade 9 she was with some one else and so was I. Let's make up some names for this, Uh, the girl I'm with now can be "K" and the grade 9 girl can be...uh..."J"? sure. anyway, I really liked "J" while i was with her but she got scared about a real relationship so we broke up. K and I started talking and hanging out and eventually dating through grade 10, K was always feeling a little jealous towards J because of how i felt previously. We started arguing a little bit and decided a break was needed so we went on the 2nd break of our relationship (the 1st lasted less than a week) this one however was about 4 months and she started talking to another guy uhh lets call him G. There was an annual street fair held in our area which I attended with a group of friends including J. That night K went to a party in which G attended and K ended up drunk making out with G and I made out with J. This made K and I vary angry and sad with eachother so we lost touch for a few months.
Summer Vacation came and things started to get better between K and I near the end, not long after school started for Grade !! she and I were back together. Everything was great, going alot better than ever before for a long time. I started texting J's best friend/my friend just for something to do once in a while if i was bored. K always was asleep early so if i was up bored I could text...D we'll say, and just talk about nothing, eventually we started texting and talking alot and I was hiding it from K because of how jealous she always got. J started dating one of my best friends. D and I developed feelings for eachother but never really confessed them but you could tell they were there. At the same time i was texting J again just as friends kinda flirting but still hiding it. I know that's wrong and i shouldnt of but i did. Summer came again and K went on a trip to Italy and I had no one to talk to but J and D. So we started talking and hanging out a lot and groups of friends including J and I would visit a Camp resort multiple times and one of the times we got drunk and I kissed her on the cheek.
K came back and things started getting out about the texting and the feelings and the kiss at a party and got to J's boyfriend, he and I broke contact for a long time understandably. He and I are cool now. K and I broke up and I felt there was no way i was going to be with her again after what I did with someone she already was so worried about with me. But after time we started seeing eachother again and everything is kinda back to normal except that I have completely lost contact with J due to I would lose K in an instant if I talked to her. J and I were best friends before any of this like ridiculously good friends.
J and her guy are still together and K and I are together and D is sort of seeing a mutual friend of us all. Lately K and I feel distant some days, and she still get super jealous if i talk to D, but never talks to me about any problems she has so i have to communicate with someone. I miss J as a friend and maybe more, there's no way i would hurt my friend/J's boyfriend by doing anything like that again and I dont wanna hurt K but i feel at times that I shouldn't be with her, but other days it feels so right. Today we were talking and shes going out of town tomorrrow (31st) with a friend of hers and she said she doesnt want me seeing D. I'm like well if nothing else is happening (party or anything) and theres something that shes doing with people than i might see her and shes like "well i dont want you 2 to get drunk and confess your love for eachother"
I understand where shes coming from but even she herself said things were getting better and i didnt expect this at all. It makes me feel like K and I are being thrown back to step one of trying to fix things after everything happened and at the same time i think like i'm in love with J and also really attracted to D who is still seeing a friend of mine as well.
I'm so lost and don't know what to do. I hope someone was able to put up with this novel long enough to be able to help and I apologize for making people read so much but I really need help.