Getting married is a public ac contrary to Catholic faith and msorals. They are right in saying they cannot be forced to retain him as an employee.
And you know what? I doesn't actually matter what I think, what you think or even what the judge thinks. This is free exercise of religion issue, and that's solid First Amendment. If a religious school says they cannot retain a person who publically violates their religious code, then so be it --- no matter what we think of it.
“as long as they refrain from publically committing or advocating acts which are against Catholic faith and morals”
That is not what they say they do. There is no “morals” clause in their hiring statement. In fact, they essentially reject it since there is no religion or creed one must adhere to - and they specifically say they will hire someone regardless of sexual orientation.
Their wording is identical to what is used in secular law, so they brought this lawsuit on themselves. At best, they were STUPID. But if you read about them and their goals, you will realize they are liberals first, Catholics second.
Their hiring statement could easily have said that as a religious institution and a Catholic school, hiring would reflect what the school believed was needed to demonstrate Catholic belief - but they did not.
They are like the anti-gun people complaining that someone broke in and robbed them.