behavior changes

Hello, my husband and I are having troubles with our five year old indoor cat. We just moved into a house a little over a month ago from a third story apartment and our five year old cat Niko has been acting strange since we moved. A little bit about him, he was neutered at three months, he is front declawed and he has always been non-dominant and very laid back. However, about two weeks after we moved he started gradually becoming irritated, grumpy and extremely aggressive towards our other cat who he has always been best buddies with. He is also constantly trying to go outside and gets irritated that we don't let him out. He has also been pulling out his fur, and after taking him to the vet and getting medication we've ruled out he doesn't have allergies or ring worm.

He will sit on the edge of the window and growl and hiss, especially when our other cat walks by. He seems like all he wants to do is be an outdoor cat, and he's not very enjoyable to be around anymore. I don't want to cause any long lasting problems with our other cat who has been getting beat up on, but he also absolutely adores Niko and would be traumatized if we separated them. Has anyone had experience with this and will Niko chill out after a while or should we just let him be an outdoor cat? We have coyotes and big fox around our house so I doubt Niko will last very long out as an overweight outdoor cat.

Any advice is greatly appreciated. Thanks in advance!!

Thanks you!! Niko was put on Prednisolone which is a steroid. I'll look into getting feliway and hopefully that will do the trick! Thanks!