Has anyone every known someone that kept going back and forth to an ex for years. DId they every realize they deserved better and moved on.. I know someone who keeps going back and forth for years.I am trying to figure out a way to convince them to move on any suggestions..

As hard and frustrating as it is, you have to back away from what they do sometimes, and realise this is how they deal with each other, and it is what it is. Crazy, but they must love it like that.

I would suggest you leave them to their own problems. I've seen this before as well.

Funny how some people can't live without some form of conflict in their lives.

Yes Me,
Me Ex left me 14 times in 18 Years. I begged her back 12 times. The 13th time I moved on and met somebody very special. She panicked and flew 1000 km's to beg me to take her and my 3 girls back. I did and ended my relationship.
The 14th time was 17th July last year. I researched Borderline Personality Disorder and BINGO it was her to a T and realised this "Splitting" and abandonment is regular behaviour. She would keep sinking the boot in as much as she could to get my attention "Hoovering".
I met someone September last year who is special and tried to move on.
My youngest daughter came to live with me (Totally unexpected for Ex and myself) and when she found out I had a newby, she flipped. I had to put a DVO on her.
Ever since then she has been trying to get us back together.
She is sick mentally and that is not me being insultive.
If you don't take a stand and say enough you too go mental.
Mind you, her continual Hoovering does remind me how much I have loved her (18 YEars together). I suffer depression and anxiety when she contacts.

I suggest you or your friend do some internet research as to what are the symptoms of the other person and decide what is the best course of action.
It does take an aweful lot of self dicipline and self esteme to stand up to things.

Google the abuse cycle. It is continual and very real.