struggle and confict

Pain - the hurting ache inside. Seems to balloon out from my head touching everything i see and do. Im moving thru a thick soupy fog and just want to be asleep - unconscious - not feeling. Its deep in my chest - truly heartache. Im sick to the stomach - it churns away inside me.
A huge tale thats hard to tell and this is the long running end part. The chapter thats trying to close but theres always a few more lines cos i keep letting them be written. As if i have no say, no power over the closure. I keep hanging on because the end means i have to lay this book down somewhere i cannot find it because i must not pick it up again. My broken heart needs to mend finally.
James ended 10 years with me. He was very unhappy with me and had met someone else. That was nearly 2 years ago and the nightmare never ended. He has a lot of Narcissistic traits and our relationship was very difficult. He wanted to be friends. We have a son. After only 4 months with her he was back in my bed. Im so ashamed i let him. I know i was vulnerable and weak and still in the throes of my devastation at the relationships end. However i have just prolonged my agony and he has lied to both me and the new woman and juggled us both. I feel like my heart is so small and discoloured like some sick shadow of a strong, beating, life giving organ. I have withered in every way from physical to mental. I have allowed myself to disintegrate.
3 weeks ago i had  another stab at "no contact". All previous attempts have failed miserably. I felt a wee bit stronger and i knew i had to get out of the terrible situation id gotten myself into. The love triangle, the endless conflict, the second guessing, all the lies he tells me, the broken promises, the pain when hes with her, the self loathing for being part of all this and the knowledge that my love for him was destroying me. Its been very hard but i felt hopeful. I tried to see him as a Narccissist and read as much as i could to help myself...... he wont change...he never loved me..... he will never love her......etc.  And tomorrow is our sons birthday and ive given in to having him here. i know i have the little box of yearning to see him still in my head. The one i try to pack away but its there. I was hoping that time and space from him would lose or empty that box for me. Its only been 3 weeks so im still in so much conflict and pain. I know it will take such a long time. I worry i cant do it. Its a mess.
I feel horrible.