oh hun I have been there. When I was 4 months pregnant my childs father left for work one day after sleeping at my house and didn't come back. It was very hard to take, he wouldn't return my txt's or answer my calls and showed no interest in Ashton. For months I cried wondering what I had done and why he didn't want to be a part of our lives. I didn't understand how someone could turn their back on their own baby. I later found out that he was seeing someone, a person who caused trouble in our relationship and constantly stalked me online, read my blogs and looked at my photos etc (I had no idea at the time) and she kept telling my sons father to get a dna test, don't be so sure it's his etc. Once Ashton was born I told him, asked him if he wanted to come visit. He said no basically and that he wanted DNA tests (which never eventuated) and we didn't hear from him for 3 months until I filed for Child Support and had to get DNA tests done. The day we got the results back (2 days before Christmas) he txt me and said "When can I see MY son". This was so hard to take, I had grown very attached to Ashton as MY child, that he was all mine and I didn't have to share him with anyone. I had gotten over the fact that his father was a jerk and didn't want him, because I did with all my heart and soul.
He has had a few visits, been in and out of his short life, and we have now moved 300km away from him which was the best thing I could have done. All in all I am so happy being single and having my gorgeous child who I love so so much.
So basically, while it's tough in the beginning, and you will be overcome with sadness, it does get easier.
BIG hugs to you.