I'd agree that obvious/direct mistreatment, yes. Only after he was possessed. But from the end of New Prophecy up until Vision of Shadows, he's just a general jerk to her. This may be only my opinion, but he is just really frustrating to read about and he has NO IDEA he's even doing it. If you look at other successful pairings, (IvypoolxFernsong, SandstormxFirestar, CloudtailxBrightheart, SorreltailxBrackenfur) There's none of this constant arguing, manipulation, and emotional turmoil going on. Some of this could be Squirrelflight's fault, but I'd say that it's mostly Bramblestar.