I got with my first husband at 16, married at 18 while still at school and divorced at 28 after ten great years and a wonderful daughter (whom I had at 22 and was NOT the reason I married)
Marrying young CAN work but, as my own experience showed, both change and if you change in different ways the relationship eventually fails. Although, if, as in my case, it was simply a matter of changing in different directions it makes a good break up and lasting friendship possible.
And, although it's not exactly on topic it does, I think kind of touch on the bisexuality issue because the reason for the change might be a growing realisation of your bisexuality and a need for a different sex partner. In my case that was a tiny part of the change but in others it might be more