Konna no Unmei ja Nai kara Kanchigai Shinaide

Yuuzen, Kouetsu, and Ginga have been best friends since preschool, and they're at the top of the pecking order at a prestigious academy for only the most elite alphas. With their good looks, money, and academic prowess, they enjoy life on easy mode... at least, until one day, Yuuzen displays symptoms of being an omega! Unable to resist Yuuzen's pheromones despite the medicine they take, Kouetsu and Ginga give in to their instincts. Taking turns, they force themselves upon a confused and ecstatic Yuuzen...
(Source: Renta!)
Includes two extra chapters.