Hi Snuf
if this is a good relationship you'll weather the storm and get through
This must be a bit of a shock but I'd try not to freak out too much.
I learned over the years that just because my partner might a mum, that didn't mean I had to be a dad - or that she (or the child) wanted me to be..
I agree that drinking would only make this situation exponentially worse.
Breathe - you'll get through this.
D