I cannot recall hearing about any Gemini-Leo relationship or friendship that turned out to be a disaster. Indeed, the isolated idea of Gemini versus Leo (considering only Sun-signs) is one of the combinations that I believe hardest in. The reason is simple: Fun. It's what motivates both these signs at a very basic level, even if they express it differently and find different channels for its fulfilment. Sure, Leo is more ambitious, dominant and pompous than Gemini, and Gemini is known for its profound love of sweet sarcasm. But the interaction between these two is so good-natured that few if any problems can remain between them for any considerable amount of time.
The differences between Leo and Gemini seem to be some of the most productive in the zodiac, with qualities that are likely only to inspire and give joy to the partner. Leo and Gemini both adore social intercourse and flirting, and may even keep up a small contest between them of who can innocently win the most admirers. Gemini is verbally creative, Leo is generally creative; they draw from each others resources and thrive in each other's company. Sex is likely to be playful and light-hearted. The only thing that can stop these two from a happy union is the gray shade of the everyday.