A. A lot of Warriors' parents get killed, Ashfur's are no different.
B. Squirrelflight didn't treat him like dirt or toy with his emotions. She tried her best to love him, but couldn't. Sorry she couldn't be forced to be in love with someone.
C. It's part of being a warrior.
So really, Ashfur is to blame for his death, for Hollyleaf running away, for Brambleclaw and Squirrelflight breaking up, for Leafpool stepping down as medicine cat.
I respect your opinion, but Ashfur going 'insane' isn't an excuse.
When did she say no one could trust Brambleclaw? Even if she did, Bramble and her had many arguments, she is going to say bad things about someone who she just fought with many times. But she later said she would judge Brambleclaw by his actions, not heritage.
He had a lot of time to get over it, and he is a warrior, he could still love Squirrelflight, but she has a mate, and he needs to get over that.
He couldn't expect to get away with attempted murder of three cats and the assistance on a leader, and just walk around without conequenses.
Ashfur never went insane, demented; lunatic, crazed, crazy, maniacal are all words for insanity, and Ashfur only ever showed them in the fire very loosely, the rest of the series he was in, he was just angry, not evil.