When do you consider an Oath Broken?
Do you believe someone loses all their Honor when breaking an Oath?
How Sacred do you hold Oaths?

For me and how my tribe operates, this all depends on the Oath being said. Though there is no exceptions on the sacredness of an Oath. However, depending on the Oath, we recognize and understand how we are as humans. Sometimes Oaths can be hard to keep perfectly. At times you will fail, and we believe, so long as you continue to try, and recognize your faults and make well on your Oath than the Oath is not broken. Though this doesn't pertain to every Oath. This would be Oaths like let's say, an Oath to your people to quit smoking cigarettes, for your health and your kindred around you. This is not an easy feat, and many struggle in quitting, and someone who would take Oath on this, would unfortunately likely struggle and have slip ups and smoke cigarettes. And these kinds of Oaths, unless outright given up on we don't consider broken. Other Oaths though, like swearing loyalty to someone, and then going and backstabbing them is something we see as an immediately broken Oath.
Of course, depending on the Oath as well for us determines of someone loses their Honor. Or maybe just some, and their word cannot always be trusted.
We are human, we make mistakes, and to some extent we believe it should be forgiven a bit, as not one of us is capable of being 'perfect'.
But none the less each Oath is sacred. And should be upheld to the best of your abilities.