You don't. No way that ends well. Assuming you like this woman and want to build a future with her, you can, however, ask her for some clarity on what role she sees or wants you playing in the child's life. Does she want you to be more disciplinary? Authoritative? Or, sit back and "chill" like her? etc etc. Based on her response to this question, you can better determine what you should or should not do and if you'll be ok playing that role, or lack of role, in his life. We answer your question as a group on TGOS 65 during the listener feedback section of the show (after 34min).