Biggest fight ever

Hey guys.
For more than 5 months I've been with my gf, and just now, we had like the biggest fight.(I think)
In that 5 months, we never fight nor argue.
NEVER.
But just now, it's like, the world has turned upside down.
I'm becoming me again.
The same guy that was a few years ago.
I don't know why but it's like when I got a gf then when just one particular thing that made me mad will suddenly change my personal identity.
It's like a life switch.
Once that switch is turned on, there's no possible way to turn it off.
Once it is on, I'll become a guy that's short minded, hot tempered, aggressive, hot blooded and so on.
I don't know why.
It happens to all of my exes and my current gf.
What is wrong with me?
I've told her that I' m not the one for her a long time ago.
Now look at us.
I made our relationship brittle.
Maybe I don't deserve to be with her.
Maybe I don't deserve to be with anybody.
Like my ex used to say,"You don't deserve to be with any girl.".
Maybe she's right.
Maybe I am.
What have I done?
Am I too blind to see my own self?
Am I too stupid to notice and wake up from this dream I've been living in?
I would do anything to reverse all of these.
Even if it means risking my life.
I would die for the person I love the most.
I would rather see her with another man as long as she's not suffering with me.
Although I will always cry inside and out when I see her with another man.
I will do the best for her.
And hope for the best for her.
I'm losing the persons that I love one by one.
Is it me?
Is it my personality?
Am I that bad?
Am I?
I wish I could make it up to you, my dear.
But what could this weak, stupid, self-centered man do for you?
I truly am sorry for all of these.
I really am.
Sorry.....