Jupiter may be the most powerful of the gods, but he also a big baby. He simply has no ability to control his desires, and is constantly off chasing women left right and center. Not that he truly loves these women; Jupiter is more interested in some quick sex, and hopefully he can get out of there before Juno, his wife, comes looking for him. If Juno does come looking for him, however, Jupiter is likely to take extreme steps to cover up his actions – such as when he turns Io into a cow. Even though he has some superficial concern for these women, he's really more interested in covering his own behind.
All the same, Jupiter isn't entirely a bad guy. For example, he is concerned with enforcing justice among humans, and especially with protecting the laws of hospitality. This can be seen when he rewards Baucis and Philemon for their extreme generosity towards guests. On the other hand, sometimes he turns what could have been a "teachable moment" into an occasion for violent revenge, as when he conspires with Neptune to wipe out almost the entire human race with a flood. In the later books of the poem, Jupiter takes on a more dignified role as the guardian of the will of Fate, who decides which mortals will get admitted to the god-club.