Need advice from Step Fathers/Fathers please

I suspect the situation you have described is making the boy extra insecure if his "real" father has abandoned them and he knows it. Children know more than we give the credit for. He is clingy.
I skimmed and I think Rusty hit it well. You must marry her to make a commitment. Then and only then will you be able to claim fatherhood. Then you and her must have the understanding the discipline will occur on your level. Mark my words in a few years you will be stupid to him. You will not have any wisdom until the young man reaches about 21.
Then if you have done your job, you will be a pretty smart fellow to him.
Hopefully his friend as well.