My (indoor) cat is stressed out daily from seeing a neighbor’s (outdoor) cat on our porch.

Our neighbor’s cat (who is very friendly and seems honestly sweet and interested in our cat) has been visiting our porch daily. Whenever our cat catches a glimpse through the window, it sends him into a hysteria.

He’ll attack the glass until we can chase the other cat off, then he’ll pace between every window in our house for an hour before he calms down. He stays paranoid because he’ll hang out by the porch window, occasionally checking until it gets dark out.

We have Feliway diffusers around the house. We were hoping he’d get used to seeing the same cat, but he hasn’t. What advice might you have for this situation?