If Asad was in fact totally out of it, and he was assualted then there wouldn't even be anything to forgive. It's not his fault. It's like asking a man if he would forgive his wife if she got raped, would he look at her the same, would he love her the same? Why not? What would she have done wrong? Of course there will be pain, a lot of pain, for both the assaulted person and their partner, but neither would be to blame, so I don't see why things should change in this scenario.
If however the person willingly slept with another person, that would be different. That would simply be cheating and I don't think anyone ever can say they'd be the same with the cheating partner. I think it would be impossible. You can still love the person, want to be with them, but feel exactly the same? I doubt it. There would be no trust.
It could also be the case that Asad was drugged but was conscious and was in control of his body, and he slept with Tanveer. In this case also, I would think of it as cheating as he would have control. This would be the same as the second scenario.
So I guess my basic point is it depends on whether the person was in control of their body or not, and if they wanted to do something or not. Depending on the circumstances the answers would be different.
Plus I don't think in relationships the words of someone like Tanveer should matter to anyone. If other people's thoughts and words are more important to you than the person you love, then you can't love them that much. But again, it could depend on the situation. If Asad cheated on Zoya, it would play on her mind, if Asad didn't then I don't think her words should hold any importance.
Anyway how is it possible for a man to be so drugged he falls unconscious by the looks of it, yet he can do the 'deed'? It's impossible. Anything that happens to him without his control, is an assault, and I hope they point this out.