Most Helpful Guy
well first just because you get married doesn't mean that you are to serious to live life. mostly in western culture it fairly common for couple to live together before getting married but after four years she has probably past the point of asking why you don't want to comment and that will defiantly increase any negative attitude she has towards you and makes your relationship harder , maybe it was you that didn't realize how rocky y'all relationship actual was.
Basically you have to set down and talk no matter how uncomfortable it may be and you have to consider her point of view and well as tell her yours. Basically she wants more commitment form you a marriage certificate and a ring to show others your are commented to her if you love her great but if the fighting drama and negative attitude has you so discussed that you can't get over it (been there) then let her know maybe she will want to try to work on it or maybe she will just want to move on.
As far as a break up while living together that can turn nasty. whose name is on the apartment lease or tittle the other one need to consider where to move but if both names your stuck until the end of the lease.
Custody of the dog now I take that as a serious matter !!! you mite need to get a lawyer and go to court for the dog0