You and your parents would be most fortunate if he didn't perform an encore of his "one-night stand" on you. Who is caring for his son; I am sure that at 15 he is unable to assume any responsibility.
You are only 15 and far, far from being an adult and you lack the ability to assume the responsibilities of an adult. So go back to being a happy and fun-loving teenager; enjoy fun with girls, outings, hikes, picnics, swimming and stay away from those boys like your erstwhile lover. Don't play with fire especially with someone more experienced and much more irresponsible than you. If there is a mistake it is you and your family who will be paying for that mistake while he can go on with his irresponsible life.