If I were in your situation and I was seriously considering adoption this is what I would do.

1) Cease all contact with the (alleged) father. Notice I said alleged.
2) Start talking to a social worker who specializes in adoptions.
3) Really find out what your legal rights are.
4) When the baby is born, do not put the dad's name on the birth certificate.

He would have to contest the adoption, and prove he is the biological father to stop it from happening. He might be too lazy or full of hot air to follow through with either, and going to court costs a lot of money.

You need good, up to date legal advice, and you need to be working with a social worker. There are too many factors and too much to navigate for you to shoulder this alone.