New cat won't stop chasing resident cat
I'm at a loss for what to do. I got an 11 month old male cat (NC) to accompany my old female RC last September and the introduction process has been shaky since. RC is not as energetic and feels threatened by NC, always hissing and growling whenever he stares or tries to approach her (even while a gate is stopping him). To her defense, NC would try to chase RC every chance he got, and I thought it was play aggression until things got serious. A few times they had physical altercations (always instigated by him), and a couple times she drew blood. I went on a weekend trip once and made the mistake of letting them have access to each other. When I returned, I saw that RC pooped in her blanket in her favorite room. She was terrorized while I was away and hid for a few days afterwards. I started the introduction process over again (after 3 months of no success) and it's been about five months since. I've done the scent swapping, closed off RC in her favorite room during site swapping (she Freaked out when I tried to put her in NC’s room), structured extra play with NC, feeding on opposite sides of the door, and training NC with commands (to hopefully use when they're in the same space).
Now, I'm at the point where I started letting them see each other in the same space and supervising them so things dont get it off hand. Well, I'm wondering now if it backfired. I swapped both cats’ blankets and RC is still defensive (same behavior) and cautious, but she's sleeping on new cat’s blanket on her favorite couch. Meanwhile, NC repeatedly sniffed her blanket and aggressively tried to bury his food before even eating it. He hadn't eaten in a while, which I found very concerning because he Loves food. He also vocalized to show me he was upset and only ate after I used a command I had been training him (accidentally, through repetition) with to get him to eat. He’s clearly feeling territorial - his eyes were big during this - and I don’t know what to do. What’s the best move forward at this point? I see progress, but I'm not sure how much RC can take given that she feels safe only when NC is shut off in his room. She's not completely bothered by his smell, but seeing him bothers her. Despite everything I've done, when he has access to the rest of the house or her, his fixation on her - or finding her - is unyielding.
TL;DR: Old female RC still feels unsafe around young male NC despite 6+ months of reintroductions and training NC. NC remains intensely fixated on RC and recently showed territorial behavior over scent swapping, while RC only seems comfortable when separated from him. I’m unsure what to do at this point.