I saw a black cat in the temple ... Is it unlucky?

There is nothing unlucky. Animals that can often stay in monasteries are all sentient beings with Buddhist affinity, especially those who were close to Buddhism in their previous lives and fell into three evil ways, so people who come and go to monasteries, especially monks, will be very close. And according to the situation you described, this black cat has a heavy fate with you, so read Buddha for it more!