Oh nottalotta, what a bummer
.
Don't worry about the "why did she get pregnant?" thing- I think that the only people who could ever ask that are those who have led very, very sheltered lives, and genuinely believe that you meet The One at 18, and get married and have kids and live happily ever after for ever 'n' ever, and that if you even consider having children outside of these circumstances it will be a Complete and Unmitigated Disaster.
Well, life doesn't work out like that. Women end up having babies in all kinds of non- ideal circumstances, and it usually ends up fine- for them, and for the kids. Or, they do have children within the White Picket Fence of Conventional Normality, and then it goes horribly tits up, and, after a horrible couple of years, it goes all right for them, too.
I'm sorry to hear about the nasty argument today. I guess only you and your DH will know whether this turns out to be a little spat, or a sign of something more serious. Is your DH open to full and frank discussions about the state of your relationship? It's probably a good time to re examine all the ground rules, in any case- a lot is going to change in the dynamics of your relationship with a baby.
But, if the worse comes to the worse, remember- having a child on your own is not the end of the world. I've been there, and I'd rather have been there with a small baby than in some of the grislier relationships I've read about on Mumsnet.