His name isn't important

In school we were taught that names should always be offset by commas:

My boyfriend, Paul, and I went to the store.

The logic is that "my boyfriend" and "Paul" refer to the same person, so "Paul" is extraneous and therefore should be offset by commas. We already know that we use commas to offset extraneous information in a sentence, so this logic is flawless.

Here's the problem: what if I have more than one boyfriend?

If I just said:

My boyfriend and I went to the store.

how would you know who I went to the store with? You wouldn't. If we didn't specify, I could have gone to the store with Paul or Art or any of the other boyfriends, and you'd never know the difference.

In this case, you don't need the commas because "Paul" is important information. It's not extraneous; in fact, the offsetting commas are extraneous. The sentence should read:

My boyfriend Paul and I went to the store.

This makes it very clear which boyfriend we're talking about, which is an important piece of information.

It works the same way with everything:

Alvin and his friend Theodore formed a band.
My sister Rachel sometimes likes to be called Sally.
That meanie Jim made fun of Junie B's outfit.

That's not to say that you never use commas in that sort of situation:

My boyfriend, Paul, and I went to the store.

In this case, I only have one boyfriend, so "my boyfriend" and "Paul" are actually synonymous. In cases like this, the information in commas actually is extraneous, so you can feel free to use offsetting commas. Because really, who cares what his name is anyway?