Hello! So,I did a big mistake a week ago when I brought a new cat home. My older cat is 5 months and the new one is 4 months old. I got introduction advice from my friend and they basically told me to just let them be together and work it out. That the agressive behaviour is normal at this point and I should just watch and make sure there are no serious injuries. A big mistake. (both of the cats are males, my older one was castrated 2 weeks ago, the new one will be castrated next Friday) I watched them for 3 hours, the new cat didn't really care about my older cat but my older cat hissed at him, and growled and swatted him with his paw. Then the older cat started to attack the new one. I asked my friend if this is normal and they just said that it's just him showing who's the boss. The attacks continued literally every 30 seconds, if the new cat dared to move a muscle my older on was biting him somewhere, mostly on the neck or on the legs. My older cat was chacing him and biting and attacking and it was horrible to watch. The new one had so hard time protecting himself. Luckily there was no injuries or blood. After 3 hours both cats were a mess, panting and all but my older cat couldn't stop himself from attacking. At this point I was pretty much panicking myself and texted my friend that truly this cannot be normal, am I supposed to watch this the whole night?? Which she replied to seperate them for the night and continue at morning. I tried again at the morning and same thing, though now I seperated them immediately after the first attack. Then I started to google stuff and well, found out I did pretty much everything wrong. You can imagine my shame for letting them do that, I truly believed my friend and thought this was normal and that they'll stop when they have settled who is boss. So at the moment i'm trying to re introduce them with Jackson Galaxy's introduction technique.They have been seperated for 5 days, I feed them at the same time on other sides of the same door. They don't seem to care about each other too much, there are occasional paw swatting under door and intense stares when they see each others paws moving, these mostly happen at the feeding time. They don't really even spend time looking under the door, mostly do their own things, but I definetly am not going to show them to each other for at least another week. (and yes I have a pet gate for when it's time for next step of introduction) I swap their places few times a day so they can smell each other. I also bought feliway friends pheromone pack thingy. I went for an 1 hour car ride with my older cat to kinda "reset" his memory a bit. Scince he's the agressive one. My questions are, did I already ruin their relationship? Is there any hope left?