I'm not going to tell my girlfriend of 8 years that something happened in my past
Is there something you are trying to hide from her?
I got laid by a lot of girls and it ended up badly, worst of all is that I had a child with them and I had to raise the child myself.
I understand that some parts of your past  you don't want to bring up, but this is too big to just ignore. Your girlfriend deserves to know such big events that will affect her life eventually. You don't want her to feel betrayed and hurt knowing that you have another family.
It doesn't matter, I'm going to go with this. She won't find out for a long time, who cares about hurt feelings.
That is unfair if you care about her. It's hurtful to hide important things from your significant other. You want to be open with her so you can build trust.