I have been separated from my husband for 5 years. We have a 4 year old son together. He does pay child support and he is involved but my son does not know him as "daddy" he knows my boyfriend as daddy. My boyfriend and I have been together for 4 years and 9months. He has been my sons daddy since he was 3 months old. Me and my husband are in the process of getting a divorce and he is willing to sign over his legal rights to our son afterwards. I want to know if my boyfriend will be able to adopt my son even if we are not married?

Course he can I have with my girl friend I only been with her 1 year an half

No he can not adopt until you are married, at least in most states, a few states will consider it but will look at the time you have been together.

I will say I am ashamed of the real father, who has not only legal but moral obligation, how after knowing and being with the child for these years he can just walk away. Men like this have no honor at all.