About what cxim has said... in my opinion, he may have said it harshly, but he was still offering legitimate advice.
cxim mentioned that you are asking for advice about your relationship with her, when your relationship with her does not affect us. It does, however, affect you and her. Given that this is a decision that direct involves and affects her, it would probably be a better idea to talk to her rather than to talk to us. Other opinions may be great, but in the end, given that we do not know all of the details, and could not possibly understand all the nuances of your relationship with her, your values, your morals, your life, your experiences, etc. it is unlikely that we could do any more than offer a set of options--however, we really do not know enough to make well-informed recommendations.
cxim also mentions something along the lines that you'll have to deal with your own problems. Perhaps unnecessarily curt, but what cxim may mean is that the answer is probably within yourself, and if not, communication with your girlfriend would probably provide more answers than here. The decision is yours.
cxim also mentions concern about her child. You also made reference to the fact that the child thinks of you as a father or something like that. If you continue your relationship for years and then leave, that could have a negative impact on the child.
These are not necessarily my opinions, however, I'm just expanding on the points I believe cxim was trying to make, of course, in a more concise fashion. I don't think he was trying to be a jerk or anything, just trying to be blunt.
I am not trying to criticize you or anything, although I do think that it is impossible for us to suggest something unless we knew everything that was going through your mind. We can't analyze incomplete data.
Best of luck.