The option when Alistair has to sleep with Morrigan is even more fun, especially if the main character has an affair with Morrigan
You mean if the Warden is sleeping with Morrigan and they convince Alistair to do it anwyay? I do think that's funny - I have no idea what arguments the Warden uses in that case - and I love that BioWare gives players the option. Options are good!
