Don't do anything stupid. This sh*tty time will pass, and you will get through it and come out a stronger and (one day) happier person.
Try not to get stressed about being a "single mummy" - it's a label with lots of negative connotation (thanks to negative commentary in the media); but loads of women (and many men) bring up families without a partner, and do a great job. In some ways it is probably easier to get on with the business of caring for your baby without the big baby (your ex) to worry about. It sounds like he is a bit selfish and self-obsessed to say the least. So forget the label: essentially you are going to be a mother, and whilst that is one of the hardest jobs in the world, it has moments when it is incredibly rewarding.
You have clearly already started to bond with your DD, but wait till she has been out a few months, and you are able to hold her and look into her dear little face - it'll be a love affair that never dies.
Becoming and being a mother is difficult, and in these circumstances I imagine it must feel daunting, but you can do it. A friend of mine recently became a mother in similar circumstances, and she is doing brilliantly and has a fabulous little girl whom she adores. Of course it has been (and is) hard going at times, but she knows she is the best person for the job.
When you have had a little time to get over the initial shock of being so unceremoniously dumped, try to concentrate on the logistics of getting through the next 6 months. As other posters have said, lean on family and friends as much as you can (are your family supportive?), find out what benefits you are entitled to, and try not to let your ex boyfriend's shoddy behaviour spoil this very precious time.
Don't forget too that you'll have lots of MNers here to talk about your baby with, and can come on at any time for a chat and advice, if that helps.