I've watched my villagers breed for a bit then noticed something strange. There were storm clouds above my villagers' heads. I logged onto Minecraft and noticed my Villagers, which I named Rose and Allen, wouldn't breed. They had hearts then storm clouds. Do my villagers hate each other? What is the problem? Do they need something specific to stop this?
From the wiki this particle indicates that the villagers are upset. In this specific situation, it is because they cannot successfully breed, due to a shortage of resources (e.g. beds):
Attacking a villager in a village; when villagers can't breed because there aren't enough beds nearby.
In older versions, this requirement still applies - villagers are limited to whatever number of "resource" they require in order to breed - in older versions (as BlueTangsRock mentions) could be either doors, or a minimum amount of food per villager, in order to successfully breed. E.g:
12w07a: Villagers now repopulate villages by the number of houses there are.