You are not an asshole. You sound very rationale about your situation and show a lot of introspection about your own history so that you don't project your past onto your present circumstances.

Your feelings of guilt is your intuition triggering you to leave a relationship that has run its course. Her pregnancy happened. That does not obligate you to stay with her or marry her. Do you know how many people do that and then end up divorced? Too many.

You already know what you want to do so I will encourage you to follow through and do what's best for yourself. That does not mean you are repeating history the way your father left. If you stay, you stay for the baby and the mother which are two wrong reasons to stay especially if you don't love her anymore (which is normal, by the way, when the relationship has come to an end for one person). If you stay in a relationship with this woman just to satisfy her, the baby and society, you are not staying true to yourself.

You can easily support her through her pregnancy as her ex-boyfriend and you can easily have a relationship with your child with this woman, as her ex. People make their own rules. Sit down with your girlfriend and lay out the plan so that you can stay true to yourself (you don't want to be in the relationship with her anymore), still be there for her platonically, and be there for your child together (as many divorced couples successfully do).

But whatever you do, don't stay with her if you're no longer in love with her. You ca be single and still support her and your child together as friends. People do that all the time.