I had a similar circumstance for 2 years. He would sit and look in at all hours of the day or night, but as soon as the door opened, gone. We fed him for 2 years, through a winter, through hurricaine Sandy. He was in the house 3 times and all three times he broke out (jumped through the screen) when he realized he was trapped. The resident cats did not seem to mind him and I suspect he was simply looking for a mate. The last time we saw him was January. He came, he ate, he walked part of the way in and then scooted out. That night we had a bad storm and freeze and we never saw him again. the best you can do is continue to offer food and hope your visitor develops trust.