I think a few of these words combined describe this relationship. I chose power because of what Willow and Tara brought to each other through their love for each other.

Willow gained magical power and ability becuase of their emotional link.
Where Tara's self belief and confidence increased empowering her in a more emotional and personal way.

I hope that makes sense to other people I think my head is a bit jumbled :)

I understand em_em, what you meant.. You mean that Willow was beginning her witchcraft in college and was less power that she learned and study from.. After her huge break-up with Oz, came to a huge force within her until she met Tara and everything change through magics...Willow's power was increasing through Tara and feels much more emotional bond with two different types of magics either good or more powerful that is in them

In the best of times, it's about empowerment. In the worst of times, it's about power struggles. As Buffy says, "it's about power".