Greek mythologyisn't usually known for its' prudery. The ancient heroes and especially the gods had many affairs, if the ancient historians are to be believed. Arguably the busiest of all gods in that regard was Zeus, the father of the gods, himself. He fathered many children, with whom he sometimes had an own affair later on.
Because you can easily get lost in all the stories, somebody published a nice infographic showing all of Zeus' affairs according to historic sources.
The whole thing looks like in the picture above. Names directly on the inside of thick black circles are Zeus Affairs while the coloured lines denote relationships between mother and child.