WildIrish makes a good point but I'd argue that you sometimes find friends to take up your partner's "slack". No person can be everything to another, IMHO. For example, I am a news junkie and my guy doesn't know the difference between the Democrats and the Republicans. I have many political junkie friends for discussions on political affairs and the like.

That's probably not exactly what WI was getting at but it was my first thought when I read it.