Oh, this is a common story with cats. One effective solution to this problem is to have the cat neutered. Have you talked to your neighbors about the problem? Castrated cats become indifferent to female cats and leave them alone. It’s not an option to lock your cat up, because if she’s used to walking outside, it will be very stressful for her to be limited in movement. I recently read an article about this, here it is https://cleverpetowners.com/male-cat-wont-leave-female-alone-what-should-i-do/. You can follow the recommendations that are written there. Maybe then the neighbor’s cat will leave your cat alone.
