Here's Karma the lovebird's story. Karma was successfully paired with the following birds: a cockatiel, 2 parakeets (at different times), another lovebird, and his last pairing was with my green cheek conure Lola. *Karma was unusually friendly and non-violent with other birds, so please do not automatically assume that your lovebird will get along with those types of birds.* Karma's pairing with Lola lasted 6 years until his death of old age. This pairing was the most successful, so I'll only go into detail about how Karma and Lola came to be "married."
I adopted Lola from Petco when she was 3 months old and Karma was 6 years old. I brought her home one night and the next morning I let them both out of their cages to interact (I know,shame on me for not putting Lola in quarantine first). Karma tried to make friends with her right away. She didn't want friendship- she wanted dominance! She puffed herself up and lunged at Karma, fiercely trying to bite him in the face. Karma was surprised, but defended himself and tried to bite her back. Their cages were side-by-side but I didn't ever let them out to visit each other unsupervised. Over the course of 3 weeks they got used to each other's presence. I continued to let them out to visit each other and the fierce lunging quickly turned into non-violent "bluffing." One day under close supervision, I let them "duke it out." I could see that they were just lunging at each other and not really biting viciously- they did tug each other's feathers though. During the course of this brief "scrap," Karma backed down and Lola established dominance. They began sitting side-by-side nicely. Lola would still lunge at him or tug at his feathers if he did something she didn't like. During their 6 years together, even during their battle for domanince, they never truly bit or hurt each other. Karma accepted Lola's dominance and decided to live by her rules. At this point and from then on, they were caged together.
Lola's rules:
1. I will choose my side of the perch first and you will sit on the other side of me.
2. I will eat out of the food dish first. When I'm done picking out the pieces I want, you can come and eat beside me. If I'm grumpy and I tug your feathers, you must wait until I am completely done eating before coming to the food dish.
3. When mama gives us a fresh bowl of water, I will bathe in it first and you can bathe when I'm done.
4. After we are done bathing, we will both be wet so I insist on preening and cuddling you until you are dry. You needn't return the favor unless I am in the mood to be preened.
5. When it's time to go in the cage, I will walk in first and you can follow me. Ladies first.
Karma abided by her rules and they had a happy marriage- they even mated several times. They were inseparable for 6 years.