I have read books that suggest that if one party really wants to be married and that is their goal and they feel that they are spinning their wheels to get to that goal with someone, then they should make their feelings known and be prepared for the answer. She may be at that point in the relationship, no matter how long you have been together. Granted, it is a threat she made and something to consider on your part as pushing to get her way, but if marriage is her goal and you show no signs of being ready for it then I think it is mature of both of you to agree you have different priorities for your future and try to separate as friends. Some people are happy in relationships for years without marriage, other's are not. This is a fundamental difference for the two of you at this point and one that simply cannot be resolved happily it seems for both parties. I know it hurts terribly for you both but maybe a break will bring one of you around, good luck!