What are your thoughts on being a stepfather ?

So I've been dating this single mother for about two years everything has been good for the most part we travel together I get along with her family and I really feel apart of her family I love our kid she just turned 10 and I met her when she was 8 she calls me step dad and dad sometimes.

Apart of me is happy but another part of me is wondering what will happen in the future if I do want another kid me and my girl have talked about it and she has made it clear she doesn't want any other kids. Somedays im like I want a kid but then another day I feel like im good. Her biological father is dead. I really dont know what to do. Any advice from stepfather of men who have or going through the same thing as me