Scratch

Important cats are always breaking rules. For example, Bluestar fell in love with a RiverClan cat. Graystripe (ThunderClan's deputy and Firestar's best friend) fell in love with a RiverClan cat. The prophesied Three set up a fake sign from StarClan to trick ShadowClan into ditching Sol. Lionblaze (One of the Three) fell in love with a WindClan cat when he was an apprentice. Leafpool (A medicine cat) fell in love with a WindClan warrior and had kits (Medicine cats are forbidden to fall in love and have kits anyways, so the whole WindClan thing REALLY breaks the rule.) Squirrelflight (Leafpool's sister, used to be a main character) took Leafpool's kits and lied to her Clan that they were hers so her sister wouldn't be in trouble. Ashfur tried to kill Squirrelflight's 'kits' but discovered they were really Leafpool's and (Spoiler alert!)

Hollyleaf killed him so he wouldn't tell the Clans that they were actually Leafpool's kits.

I'm sure there are plenty others, too, but here are some examples. xD Oh, and Crowfeather fell in love with Feathertail. Then when she died, he fell in love with Leafpool, and then she went back to ThunderClan and he became mates with Nightshade. Nightshade was the only cat in WindClan, Crowfeather's Clan. xD