Steve,

No, I am sure you have not done any long-term damage.  However, you
have learned the lesson that many others have faced -- that is, we let
our emotions overcome what our brains tell us about the importance of
slow introductions.  People sometimes have success by just putting two
cats together almost immediately, but that can also be a recipe for
disaster.  It is much better practice to keep the cats separate for
awhile (as you originally intended) and very *slowly* and *gradually*
accomplish an introduction.  When I first adopted Duffy, I had to be
very careful because Holly had always rejected any other cats.  This
was a different situation, of course, because these were two adult cats
and Holly had an established history of attacking any other cat that
was close to me.  However, even that problem was overcome -- but it
took a lot of patience and the necessity to overcome the desire for
quick results.  One of the most important tools I used was to
temporarily replace a door to one room (the room where Duffy stayed)
with a door that we modified with a metal mesh panel at the bottom of
the door.  We used the hardware from the original door (door knob and
hinges) and eventually reversed the process and replaced the original
door after Duffy and Holly were acclimated.  The purpose of this door
was to permit the two cats to see each other and become comfortable
while in "almost" contact but not permit them to get into a
confrontation.  This worked extremely well!  In particular, I could see
Holly move from a posture of anger to acceptance to actual interest in
Duffy.  Incidentally, an inexpensive screen door would work just as
well.  You might also find it beneficial to buy a couple of Feliway
diffusers and use them in the rooms that the cats most-often use.

I recently had another lesson, myself, about how important the slow
introduction can be -- together with a small lesson on misplaced
aggression.  It has now been more than 2 years since I adopted Duffy,
and my two have blended beautifully -- or so I thought.  However, I
added a sunroom to my house this spring.  All went well until the last
week of construction.  Neither cat "seemed" to be bothered by the noise
of construction.  However, during that final week, Holly suddenly
started to attack Duffy.  Poor little Duffy was not injured, but he was
truly frightened and would immediately scramble under furniture to try
to escape.  This was definitely not "playing"; the noise and constant
disruption of our routine had apparently finally caused enough anxiety
that Holly reverted to attacking other cat (in this case, it was Duffy
who was under attack even though he nothing to do with the change in
routine).  Since Duffy is blind, he was suddenly at a great
disadvantage in the confrontation.  At first, I made the same mistake
you did.  I separated them for a day and then permitted them together
again.  Big mistake!  Holly attacked again, and I could see that she
was really angry.  Duffy, of course, was completely intimidated.  So, I
started the introduction process all over again.  It did not take
nearly as long as my original introduction for the two cats, but I did
go through all the original steps -- separate rooms for the two cats,
bring out the temporary door with the mesh panel, feed the cats in
separate rooms but on plates placed very close to the door so they were
eating in close proximity, and bring out the Feliway.  I am happy to
report that everything is "normal" again, and the two cats are once
again close companions -- but this shows how important it is to proceed
slowly and monitor the situation.

By the way, I always laughed because it was Duffy (my little blind cat)
who would literally stalk and pounce on Holly (who is actually larger
and stronger than Duffy).  Duffy, of course, just wanted to play.
Holly would either enter into the game or haughtily leap up to some
surface where Duffy couldn't find her.  During the period following
sunroom construction when Holly began to attack Duffy, he suddenly
learned just how powerful she really is and he was quite frightened.
Now that things are back to normal, Duffy is once again prancing around
with his tail in the air and is back to his old game of stalking and
pouncing on Holly!

MaryL

Very interestied in yoru post - as we had 2 brothers (just domestic
shorthair moggies), one of whom ran away (rather than died), and we were
thinking of getting a kitten (a Burmese, coincidentally) to offer some
companionship to Khamun - although he doesn't seem to have missed his
brother too much., but they didn't seem to interract much when they were
together so maybe that's the explanation.  Khamun is a very calm cat so I'm
hopeful that the introduction will go OK - he doesn't seem to get too upset
when a neighbouring cat comes in through the catflap and eats his food.
Although he does the same to him so he can't complain much...  Are Burmese
quite a nice active breed?  I find Khamun rather docile sometimes.