Gemini is an air sign, which in astrology means it's mental, loves to think and create. He's very curious, very communicative. Taurus is an earth sign, which in astrology means it seeks stability and order, a sense that life is in control.
These two are attracted to each other immediately, because Taurus loves the quick, versatile, curious mind of a Gemini. Gemini also loves to have sexual hi-jinks. It's very good in bed. It can titillate. It can captivate and seduce. Gemini in turn is very taken with Taurus, because Taurus has such strength of character and seems so deep and stable.
Then the difficulties arise, because they have different approaches to life. Gemini wants to not be tied down, wants to be out there, to experience, to meet new people, to have a life that's very open and spontaneous. Taurus likes something that is more ordered and has a structure to it, and is safe financially as well.
So their energies go in different directions. Long term, they might work these out, but in general there is a lot of work in this relationship to make it last.