getting off the roundabout

Its been a long time since I posted.I was hoping I would never have to post anything relating to my exN ever again.However I fell right back into his grasps.Its definitely time to leave the roundabout at the next available exit and find the right road I need to be on.
My involvement with exN has now been ongoing for almost 9yrs.During that time and right up until I write this he is still involved in some way with his ex the one before me.18mths ago he went back to her after being with me for 5yrs thats when I found this site ...to try make sense of WHY? I tried so hard to forget him did lots of reading joined nightclasses,kept myself busy.......stayed NC for 6mths ...then I made the mistake of letting him back in and believing yet again his lies. He told me ...he had had his head messed up by other woman etc etc how it was a mistake to go back ...all the right things he knew I wanted to hear ....and I fell for it.
We had a few months when it felt good again to be with him.Then he began contacting the other woman as a friend. I agreed it was ok to be friends with her as long as there were no lies about his contact with her.
Over the last few months his brother became ill and he was away looking after him everyday he phoned me for moral support and an ear as he found the strain of looking after his brother very hard.
I went away during the christmas holidays and whilst I was away he rarely answered my calls or txts as he said he was coping with looking after a dying brother.
When I returned he stayed at my house for 5 nights had his children over at mine for tea twice.
Then I discovered whilst I had been away he had been to a concert with the other woman at the very time he was supposedly looking after his dying brother and too busy to call me.
I let him know I knew this just after enjoying a lovely meal in a restaurant. I asked him if hed enjoyed the concert.....He said he'd forgot to mention it to me ....at that point I just stood up and left him there...he txted me to say ...."I didnt think you could be so cruel but no problem ADIOS" and that was it ....a week ago now .....
Why why did I go back .....rinse and repeat.....I have to do myself a favour now ....NC ever in any shape or form ....I feel nearly right back to square one ....although last time I was suicidal ...this time I am not going to let myself sink that low.