Housebreaking the Great Pyrenees?

I fell in love with a Great Pyrenees I found roaming the streets. The soft white fur, brown soulful eyes and loveable disposition set my little heart a flutter. When I returned him to his owner, they said they were trying to find someone to take him. They gave me his papers and tags and assured me that he was housebroken.

He marked my house only four steps in the door. He continued marking and the urine turned blood red within an hour. After treating his bladder infection with antibiotics, he continued to mark all over the house. No matter how closely I kept an eye on him, he was always waiting for a moment of distraction to wander off and mark everywhere.

I decided that if he was sneaking off to mark, i would just tether him to me so he couldn't sneak off. The day went perfectly. We played. We snuggled. I took him out in regular intervals and praised him every time he went potty outside.

The day was drawing to a close and I was having an conversation with my mother when he lifted his leg and relieved himself all over and inside of her purse. I caught him in the act and took him outside, but he had nothing left. When I reprimanded him for peeing in the house he became very fearful and started running from me. I think maybe his former owners were the kind to punish for the mess and not correct the act. I don't know if there is a way to undo that.

I can't help but feel angry and betrayed. I've had enough dogs to know not to take this personally, but where do I go from here? Am i going about this the wrong way? Should I keep going and stay consistent?

I have to emphasize that other than the marking, he is an exceptional dog. He's sweet, obedient, good with kids, laid back, etc.