hello Jon,
Sorry about your delema.
This is a situation that is best (in my opion) Handeled by following your hearts instincts. I believe that as death ends a marriage with it's vows and promices, as also it dose with a pact made with close and best friends. A promise of that nature and at that time may have been for your peace of mind at that point and time of grieving for you both. The pourpose of your promise may have been for that moment it sounds more like you two were trying to promise not to die on each other in that way any time soon. The promise had a deeper meanig than it's literal meaning.
I hope you understand what I'm trying to say, And again I'm sorry about your situation follow your heart sometimes the mind thinks too much and requires too much time to decide.
SennaBras