Purple firefish pair behaviour

[Javeo]

I bought these two firefish almost 6 months ago, they were not sold as a pair but the LFS said they had come in together. They were ok for the first week, then the larger of the two starter attacking the smaller and not letting it feed. It rapidly lost weight. At this point I dumped the bully for a month and allowed the smaller one to recover, which it did. I reintroduced the big one and since then they have been ok again.
The funny thing is that during the day they stay far apart from each other, and the bigger one does intimidate the little one but no physical aggression.
They now both feed together and as the pic shows they have a sleeping area that they both share and dig a small depression in the sand together before bedding down for the night.
I've read various accounts of pairing these fish and how aggressive they are, but none that relate to my situation. Are they a pair or simply two fish that sleep together for safety? The rest of the stock is very peaceful, and the big firefish is brave enough to chase the damsels and anthias. The most aggressive fish is my male parvirostris

[Javeo]

http://i96.photobucket.com/albums/l167/Javeo1/IMG_0605_zpsppwle19c.jpg (http://s96.photobucket.com/user/Javeo1/media/IMG_0605_zpsppwle19c.jpg.html)

[rtparty]

In my experience and research, unless they're truly a mated pair they won't last. One will kill off the other.

[Javeo]

That's my point, their behaviour is so different from everyone's experiences that I've read. There is no aggression between them, at feeding time they swim together and feed together, at night they both retreat to the same place and dig their little burrow and they even seem to wait for each other. The large one has a pointy fin, the smaller ones is rounded.
My question really is, is this how pairs behave? The large one simply moves towards the smaller and that one will move away. That's the limit of their aggression, it's more like respecting space then aggression. Both are well fed, active and out all the time.
If I just posted the picture you'd easily believe they were a mated pair.
http://i96.photobucket.com/albums/l167/Javeo1/IMG_0609_zpsz5pk6bsm.jpg (http://s96.photobucket.com/user/Javeo1/media/IMG_0609_zpsz5pk6bsm.jpg.html)

[Javeo]

No more ideas/opinions?

[jmm]

I bought four. They slept together like stacked logs and ate together. For about two weeks. Then one was killed. Two weeks later a second was killed. The other two have been together for about four years now, sleeping together and eating together. They're not out a lot unless they see food floating by.

[Javeo]

Thanks for the reply! How do they behave towards each other during the day? Do you think you have a true pair?
As I said, mine fought initially, to the point I thought I'd lose the smaller one, but since separating them for a month they are really well behaved. Unless the bully leant his lesson! Lol.