When Will My Cat Get Over The Kitten?

My cat is over three years old and still does not like the kitten. When I first got the kitten, she was about a year old, and she took to him right away. But now that he’s older, it’s been two months since we got him home from his foster mom (she wasn’t willing to take him), and my cat still avoids the kitten. I know they need time to get used to each other but it seems like it should be easier than this?