Get ready for a lecture.
I think you need to hear this from a woman. Your girlfriend is a slut, and you are an absolute fucking moron.
You're only 17. How the fuck are you going to support someone else's kid? Flipping burgers gets you nothing. You're both gonna end up dropping out of high school, having no money, and going on welfare, stealing from those of us who work for a living. Speaking of those who work for a living, I doubt your parents are pleased. They wanted to raise a son who makes good decision, not one who can easily be swayed by the high school whore.
Why are you with her if it's someone else's kid? It's not loving, and it's not noble. It's stupid. The man who should be responsible for the kid is the actual father. If he's not man enough to take responsibility, that's his problem, and her problem, not yours. If she didn't cheat on you, and hooked up with you after breaking up with him, I bet she wanted a "daddy," not a boyfriend. If she cheated on you while you were with her and you still love her, well, that's just fucking stupid. She's gonna do it again and keep pumping out kids.
Someone brought up the question earlier as to why this doesn't bother you. You said it doesn't need to be addressed. Yes, it does. Your avoidance of the subject tells me that you are too immature to be a father, let alone be in a relationship. Also, if you're gonna tell us you're a father, then you'd better be prepared for the onslaught of questions.
Now, if you DO want to take care of this kid, be a man and get the fuck off the computer and help with the baby.