Not to be flipant.. but .. bang her sister..
I always advise guys to not get married until they are 30yrs old, there are a lot of reasons for that..
You are young, your life before you, live and experience it. You got off lucky, you could have gotten her prego, and then kicked you but taking 30% of your pay for the next 18 yrs..
There's no figuring it out man.. The problem is for the last 4 yrs she is all you have had your life wrapped around.. let it be a lesson, let your schooling, or your job or something else other than a person be your center, that way you can have some sense of control and decisions on what your life is like...
Good luck, congrats and condolences.