Can i adopt my Stepson?

I am a 23 year old woman wishing to adopt my 8 month old stepson. His mother dumped him at 11 weeks old and hasn't seen him since. She has shown no interest in her son and expresses no wish for contact with him. She did not show for any previous legal proceedings which has resulted in his father having full parental rights. We have spoken and he has said he would be more than happy for me to adopt in the future. The only problem being is that i have been told we must be married for me to adopt. Is this right? Or am i still able to adopt my stepson?