But how could he gain pleasure? Since he says in the confession of Act 2 that he associates sex with disgust and is happy if Tav proposes a relationship without sexual intercourse? From what I understood, sex hurts him, and he slept with Tav just for manipulation. Maybe what he says that he didn't sleep for pleasure is just that he couldn't achieve it and in the end he was only doing it for profit. After all, he says that he has not had a moment of pleasure in these contacts for 200 years.
If he didn't feel any gratification then he would have said "I never slept with your for pleasure". While doing it with his clients he was often physically repulsed by them, became completely numb over the years and disassociated. After his first night with Tav, if he's told that there would be nothing more happening again, he says that night was special to him. So I believe it was the first time since many years that he did in fact enjoy it.
In the post-Yurgir confession he admits he is attracted to Tav's looks.
What is tainted to him is the fact that up until that point it was always a transactional exchange and that it was done for his master, he's struggling mentally with flashbacks. There is a similar thing happening in Fenris romance in DA2 - he gets so close to Hawke that he starts remembering his forgotten past and it makes him panic. He also needs time to figure things out before he can be intimate again.
