It sounds like something is triggering this behavior since it appears to run in cycles. Maybe he is getting overstimulated by soemthing outside or with the other cat and now the behavior has gone on so long it has become a hait for him. If you're willing to put the time in, you may want to isolate him or crate him for up to 2-3 months to break the cycle and see if you can retrain him. Being parents, whether for felines or kids is never easy, but we also can't give up on them either.
Good Luck, let us know...

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