I don't know what I want

Yesterday was my Fiancee's names day, a day that means alot to her due to the relationship it fostered between her and her grandmother, but not coming from the same backround i underestimated the importance of this day. After a meal out and a couple of drinks with her family they left at about 2130 and after that my fiancee got very sullen and started taking it out on me, she was dragging up things from the past and present, saying that my proposal to her was a lie and that we never go on holiday and generally taking out her frustrations on me, this isn't the first time she's done this in our 6 year relationship, on the walk home i massively lost my temper shouting at her to F* off and that i was sick of it. I then stormed off ahead to our home, picked up a bag of clothes and left before she arrived to go to my sisters to crash there. This morning I am in pieces, I love my fiancee with all my heart and will bend over backwards for her, but I can't handle being an emotional punching bag for her when others get her angry. I have sent her two (rather long) texts and went home early this morning to write a letter to her explaining that I'm sorry about what happened but that we obviously have issues that we need to work through perhaps with some outside help. I'm really scared that I have completely destroyed any chance of us reconciling, i don't want to loose her but i'm afraid that my actions can't be undone. Any advice?

Tell her. Sorry and tell her how much you love her. Show that you were the cause of all the problems. Act guilty. Make her feel sorry.