Your girlfriend
certainly has a foul temper and to me, this behaviour isn't
particularly surprising, considering how much you give in to her. I
am not saying you shouldn't give in to your Love, but to give in
blindly upon infinite occasions over a period of four years will
make her gradually adopt an attitude, which will NOT only serve to
take advantage of your good nature, but also proliferate the
intensity of her nonsense over time.
It is more like a personality problem, than a compatibility
problem. That's probably the reason why communication fails. If she
has a string of exes that lasted for mere couple of months each -
very likely, there is something 'wrong' with this woman.
***
I remember when my
tu di entered into a
relationship with this Pisces girl, who had scores of man before
him, and I witness how tormenting the relationship was, even though
his relationship lasted the longest among them.
I warned him: 'There is something about her personality that makes
relationship difficult. If all those who had tried before and
failed to change her mindset and everything else, what makes you
think you could succeed? I am not here to discourage you from your
relationship, but it is something you must put into
consideration.'
He told me 'True Love conquers all.'
Yunhaier looked at him and smiled. 
***
First Love? CloUdiSm
has this theory which states that people's endurance in
relationship is inversely proportionate to how many relationship
they have. The more relationship they undergo, the less endurance
they will have for their relationship, thus our endurance for
nonsense is usually the greatest in our first love or the first
relationship that matters alot to us. Our patience erodes with more
meaningless relationship we have, as we gain an attitude of
giving-it-up-easily and searching for new potentials whenever we
encounter some complication in our relationship. We also become
emotionally defensive, unable to give ourselves fully to the
relationship.
You are someone, but in the process, you become somebody else. You
altered yourself so that you could fit nicely, without disrupting
her sanity and ruin this relationship.
What kind of Love are we having here? An one-sided affair? With you
trying to hold on so much... and probably only you wanting to hold
on?
A relationship with yourself perhaps? 
Communication... where has the communication gone to?
Have you gotten to the root of her personality disorder that is
causing so much distress to the relationship? Her negative
mentality? Have you sought ways to repair those useless message
saved by her past experience? It seemed that you have spend more
time, in trying to appease her, fearing that the relationship may
be destroyed the minute you fail to do something that makes her
happy, than to enlighten, share, work things through what's really
affecting this Love - her core personality.
Then again, my question to you is: what kind of Love are we having
here?
This reminded me of a story, of an old man who is asked to quit
smoking because of his ill health, but chose to continue the habit
because the withdrawal symptoms 'kills' him faster than his weak
health. He's already so old, smoking for decades and therefore,
don't even have the physical strength to challenge those withdrawal
symptoms. Seriously, the withdrawal effect could claim his life and
since he realise to give up also die... don't give up also die...
then smoke lor.
You are in the same
predicament.
It's probably a little late to decide on anything without the risk
of her saying 'lets break up' and you begging her not to. So
instead of enraging her, you just let her do what she wants...
leading to your current sorry plight. I understand your desire to
marry her, but if you were to marry this problem into your
marriage, even without checking your birth chart, I can probably
tell you that divorce is around the corner.
If one cannot
solve his BGR problem in a relationship, a marriage cannot change
anything either.
P.S: To break up with you don't necessary mean that you have to do
something bad to her. If she wants to go... she will go. This is
our freewill in relationship - you are just delaying the
inevitable... the fact that she wants out, with you holding on for
as long as you could bear. 
Cheers