Re: Fighting Cats I need help!
Welcome, and we can help identify your problem, but the 'fix' may take some time.
First, you need to understand that the kitty (#1) who has returned DOES NOT SMELL like the kitty who originally left, so kitty #2 WILL NOT RECOGNIZE him due to him not smelling the same.
Next, you need to seperate the cats. Every day (or every few hours) switch the cats in/out of the rooms you are keeping them in so their scents intermingle. You can hurry this along by using two small-ish towels and rubbing them over kitty #1, then rubbing both over kitty #2 and repeating this back/forth a few more times and then leaving each kitty one of the towels to become familiar with the scent.
Finally, let this take the time it will take. Do not rush it. After a bit of swapping scent with the towels, and trading back/forth who is staying where, begin to crack the door so they can sniff noses and maybe play footsie (if they are interested). If they are, and it goes well, then you could open the door just a little more (I like to keep my hand on the edge of the door and use my knuckes at the door jamb to hold the door open a specific width) so they can sniff noses and have more eye contact. When that goes well, then you can see about letting them see each other more fully. Sometimes, feeding both treats in sight of each other but apart, can help get them past their 'animosity' while they enjoy their snack.
Best of luck,