Asher doesn't like lying to Sasha. But he doesn't know what Sasha will end up deciding happened if he doesn't and-- he wants Sasha to be happy, he wants Sasha not to be worried, Sasha would be so scared if he thought that his drink was drugged or he took something illegal. He just wants to nudge things onto a path where Sasha is happy and not frightened and had a good time.
In a few years he'll turn Sasha and then Sasha will remember everything clearly and they'll laugh about it.
"Yeah, you had a couple of drinks, remember," he says. (He's not looking into Sasha's eyes.) "You're definitely drunk. Don't worry, you can have fun with the guys here, I'll make sure you're safe."