1. He believes he has witnessed his son giving Spacey a blow job. 2. He adores his son, but homosexuality is not acceptable. 3. He beats up his son and kicks him out, after extracting the (false) confession that his son is gay. 4. He is now convinced that his son is gay. 5. His son leaves and 6. In a completely shocked/traumatized state he goes to Spacey's house and kisses him in an attempt to be part of that world to which his son belongs.
By the way, I don't think there's a clear case to be made either for queerness or not; I like my version because it feels more human and less stereotyped. Also, the director was English and a great deal of the movie argues, in a lot of ways, against stereotypes.
Best,
Joanna