Your boyfriend who promises you'll get married ... someday.
My boyfriance is finally planning to propose to me!
What a girl calls her unofficial boyfriend. It is derived from comparing the situation to an engagement, which is much like an unofficial marriage. In this case, the two people are not officially boyfriend/girlfriend, but they both know they will be in the near future, much like how the fiance and fiancee know they will soon become husband/wife.
My boyfriance is taking me out on our first date next month.