Sacred Haven of Debauchery

Not at all necessary. This is true for a company of half a dozen people, one of whom doesn't understand anything from the conversation, but not for two.

But there are cases when the interests of another person are not able to interest you (sorry for the tautology), for example, few girls will want to discuss Warhammer (a bad example, I know). Therefore, it is better to have common interests as well.

By the way, about BG2:
Did you know that fans are creating a conversion of BG2 into Dragon Age? Moreover, the companions look very similar to their portraits (and not only them), but only the first chapter is ready so far.