Ok so my ex went back to his ex. They were their first then after a couple years got separeted then got back together for 4 years the last year and a half she was abusive physically and verbally after he got back with her after she cheated on him. He wasn't himself and she didn't like it so she became mean. They finally broke up and after a few months he got with me for 6 months. Everything seemed perfect aside from fighting here and there.

Him thinking I didn't care or love him and thought I was mean sometimes but nothing too serious like with his ex. Anyway we broke up and days later he's engaged with his ex and after trying so hard to talk things through he wants nothing to do with me and is now very cold and mean. As if we were never anything.

When we were dating I was his world and he was mine. Now he's getting married next year in the same setting we were supposed to get married in. Could it be serious? Or can his ex be his rebound? His easy way to forget about me? Or maybe I was the rebound even if they had been apart for a few months before he got with me?

You were the rebound. He hadn't had a chance to heal from her and untie the ropes that bound him to her before you came into his life.

Well how long does a person need? I think they were apart for about 6 months and they weren't officially broken up yet but they weren't living together anymore and for the last year and a half he kept his distance.

"they werent officially broken up yet"

Did they phone each other, text, talk in person? How enmeshed were their lives at that point?

Was he willing to move on without her?

I think you were the rebound.

He was willing to move on without her but they kept incontact because she wasn't taking it well and he was afraid she'd harm herself and didn't want that on him. I guess my real question is if he went back to his abusive ex that quick and are already engaged is it possible that she may also be his rebound? I know deep down but didn't want to admit it to myself that I was a rebound.

There are no rules and timelines for how long a person needs to recover.
"Everything seemed perfect aside from fighting here and there"
"Him thinking i didnt care or love him and thought i was mean sometimes but nothing too serious like with his ex."
I don't think it was perfect at all. He wanted perfection - never a good idea, because it doesn't exist, and that might be one reason why he goes back and forth.
On your part, I wonder if you don't realize that maybe your fighting was more serious and mean and unloving than you thought. Some people thrive on fighting and that's what they saw growing up. Other people are horrified by it.

Well my question to him which he never really answered was if I were that mean and uncaring why go back go something worse rather than looking for something better? He probably can't handle being alone.

I don't believe he ever let her "go" out of his life -- so no, she was never a rebound. Only you were, and a temporary distraction.

Some people, for whatever reason, embrace chaos and thrive on it. I'm guessing both of them are that way, maybe had grown up in chaotic households and really don't value anything else, don't understand that there is a better way to live.

I have a sil like that. She grew up in a wild and crazy household with parents always at each other's throats, having affairs, etc. My brother (her husband) is a very placid person, but she doesn't allow their household to be placid and now involves their children in all the chaos she creates (and has taught them how to create it). My brother spends a lot of time working at his car wash, not wanting to be at home.

Ouch. But the truth hurts.

He comes from a broken home. He wants better but he's not really running away from the bad neither. His life. His choices. Now I just have to accept I was nothing to him and let go.

I don't think you were "nothing." I think you were the escape for him, the steadiness, the anchor he needed for a full life, but his need for chaos won out.

Only counseling would help him realize what he gave up when he left you and went back to her.

Its not that you were nothing, just you guys didn't work because he wasn't happy and healthy enough for a good relationship with you.

It happens, and hurts lie hell now, but you can be happy and healthy without him, while he is likely to catch hell with his ex.

Wish it weren't like this.

I'll look at it as having done some good for someone thatvway I don't feel so used.

I want to say I hope so, but I love him enough to wish them well so that he can be happy.

You have to give it a positive spin, or you will kick yourself until the end of time. Just don't fall into the habit of trying to lead guys out of a chaotic life. Don't become a "rescuer."

Trust me, it hurts as bad when they dump you for an ex, or you find out a years later you just aren't compatible.

Thank you all for your words.