Exclusive Secondary Groups

[QueenLionors]

Hi, sorry if this has been done, I might just not be able to find it (been searching online for a couple hours.)

Here's the problem:

Our website is for significant others of sailors in the US Navy. As such, we have specific forums for Wives, Girlfriends, and Fiancees--visible only to those in a group named the same.

A recent problem seems to be the girls becoming engaged or married, and having to change groups. They simply add themselves to a second group, and complain when they're abruptly removed from the outdated one.

So I'd like something that would set these three groups to be exclusive of each other. Is there a way to set them up so that membership in one would have any membership in the other two expire in maybe a week?

We're on 3.6.0, hopefully upgrading to 3.6.1 soon. I'm sorry we can't pay, but we're a non-profit military support site, so money is really tight.

Thanks!