Willow and Tara were probably the most sexually active couple in Buffy history. They were just never shown doing anything. Tara, was not this meek little "lets just cuddle" type of a woman. Tara *liked* sex. A lot. You can tell just by the episodes "Once More, With Feeling" and "Seeing Red." In both episodes, Willow is preforming on Tara, and Tara starts is. Plus, you can't forget this famous diologe in the last 10 minutes of "Seeing Red"
Willow: Hey, look, clothes.
Tara: Better not get use to it.
Willow: Mmm.. yes ma'am.
In conclusion, they liked to have lots and lots of sex. It is a way they expressed their love.
With many orgams.