Why do the spouses of bipolar take all the abuse?

Hi-I've been with my husband for 7 years.  October 2007 he was diagnosed with Bipolar.,  I have studied this illness.  Can someone help me understand why they are so abusive and degrading to their spouses but outside of the home everyone just loves them?  I read the article...Along for the rollercoaster ride.  It mentioned that if one more person told me how wonderful my husband was...I would vommit.  My husband is at work more than at home and I don't know why I'm so verbally abused when he doesn't see me that much.  Do they save it up and then open the can of Woop Ass on the spouse?  Prior to October 2007 I thought it was just his personality but after the diagnose it all makes sense.  He was on meds but went off and things got hecka BAD.  The rage before I compromised but after the meds - I should have headed for the hills!  No one deserves to be treated like this!  Well, he left in the travel trailer on July 31st!  My heart mourn because the person I so fell in love with died!  The one who left July 31st is a  stranger that is not welcomed back unless  proper medication and counseling is in  the works with  me & the family