The sometimes stammering and unsure Tara met Willow at a school Wicca meeting. Since Oz had just recently left UC Sunnydale, Willow was free game and ready to explore some new interests. The two immediately hit it off due to their common interest in witchcraft and casting spells. Apparently, Tara is the daughter of a very powerful witch who died when she was a child. Unbeknownst to Willow, Tara was also said (due to a family myth) to transform into a demon while developing into a full-fledged woman. Thankfully, for both parties, that was just a lie told by the male members of Tara's family to keep the little witches in check.
As their relationship started to blossom, they fought against the voice-stealing Gentlemen and their combined effort of spells saved Sunnydale. However, it did take quite a long time for Willow to admit to her friends that she had found this gay partner. The result, Tara got a little angry and then they finally outted themselves to the Slayerettes. Tara was immediately welcomed into the gang.
The only other real relationship rift that Tara was confronted with was Oz's return to profess his love for Willow. Fortunately, Willow explained to her former hairy boyfriend that she was in love with Tara.