They got along for 3 days. Now. ..

They are fighting and both are freaking out. What could've happened?
Weird thing is that they behave and get along for a while, then the fur starts to fly again. They can't seem to decide how to be with each other.
What can I do for them?

We are lacking some infos here. Sexes of the bunnies? How old are they? Are they neutered / spayed? How are they housed?

Please provide some more info like their living quarters and what you have done to introduce them. If you just put them together in unneutral territory then it's not surprising that they are fighting but I'm not assuming you did that. Anyway bonding bunnies takes time and is not easy. Check out thebunnychick.com for some good reading on bonding.

Thank you. They met at the shelter when I took Groucho to see if we could find a new companion. They got along right away. Groucho is 4 and Buggs is 1, according to their respective shelters. When I brought Buggs home, Groucho immediately loved him and perked up. He had been moping since we lost Bugsy. So, they hopped around and played and groomed each other, occasionally stopping to hump each other, each trying to be dominant. Groucho is used to being very dominant, as Bugsy was very submissive. Oh, both male and neutered. It's funny. They are both in the cage now and Groucho is worrying over Buggs because I held him and took him to meet a neighbor. Groucho always worried over Bugsy when I'd hold him. Groucho doesn't like human affection. So, I guess it worries him when the other buns get it (Buggs is super affectionate). They are fine right now. Have been for hours. They just get into worrisome scuffles every so often. At this moment, Groucho is cleaning Buggs like crazy because I held him for so long. Their behavior is so confusing!

Update:
No incidents since I posted this. In fact, they've been snuggling. Perhaps they worked it out?

Every bonded pair has their moments. We had 2 females that got along for 5 plus years and then one day they went at it full tilt and were fine the next day. I need a "crystal" ball most of the time, anyway.

Scuffles and 'coups' are pretty frequent between males, even bonded. Even if the bonding work, it will probably happen again from time to time. That's why male / male is not a recommended pairing and that I'd never attempt it ever - I find an unstable hierarchy too stressful for the owner ^^.

They are good buddies now. In fact, no incidents since my last report. Not even trying to hump each other! They snuggle in their cage, but not when they are it like Groucho and my poor dear Bugsy used to. I don't think Groucho will ever bond that completely with another, and that is ok. Buggs sure has personality! He claimed a spot on the couch and will just hang out with me for hours. If I ate something he wanted, he'll lick my face trying to get it. He loves attention. He's a great fit for our home.