What does a roller coaster relationship mean?

[Rini006]

My current crush had a bad break up. They were in a relationship for 1 and half years. They were dating and it seemed to be fine. when he graduated, they broke up because he moved out. They got back together 5 months later and he was insecure and could not find a job but after 4-6 months later they broke up again for good this time.
when I read what his ex wrote, she said it has been a rollercoaster. lt was filled with disappointment and hard these few months. Plus my crush always threatened to leave her.
When I met my crush, he was cold, pushed me away and mention that girl each time sometimes he was aggressive in his words although he was interested. So I dug deeper to understand him and found that 2 years post break up, he couldn't move on. I managed to get him out of survival mode and start living again. He speaks about me with many of his close friends which for me is good sign that he has finally moved on but I find it weird how he talks to me in indirect ways (is this part of roller coaster relationship?)
since I managed to make him move on, I am confident that slowly and surely I will be able to pull him closer. But can anyone explain to me what is a roller coaster relationship?

[Elsa143]

Screw your crush. He is still in love with that girl. He himself don't know what he wants. Don't you see that he pushed you away so many times? Why did you kept going back to understand him? He was toxic to his ex girlfriend and will treat you the same way sooner or later. He's just glad that some girl was consistently behind him and he decided to tell about you others. It's nothing special. He's just returning 20% of what you did for him. Don't get me wrong I've been in love too but these kinda boys don't deserve our time, attention and sympathy because one day they will hurt you. We're just back up option for these guys.

[1stranger]

I'M VERY CONFUSED. WHO BREAK UP FROM WHO?

If I think of a roller coaster, this concept might mean that relationships are ups and downs like a roller coaster.

[Rini006]

It's my crush, his ex girlfriend broke up with him saying it was a rollercoaster.

[Anonymous]

One of you both goes up and down and affect the other. Often has one person in such RL borderline or is bipolar. Sometimes it's just hatred-love, where people fight against losing control in a relationship.

[winterfox10]

It means that the relationship is chaotic. It's not usually regarded as a positive thing to say.

[JSmuve]

It means that there were a lot of emotional ups and downs.

[Anonymous]

It means the energy is not consistent. You’re not happy or sad for extended period of time. There’re lots of ups and downs.

[Iron_Man]

Highes and Lowe’s ups and downs