I came inside my ex-gf multiple times without telling her or her finding out
Why would you do this to her?
She didn't deserve it.
It is so wrong to ejaculate in a woman without her permission. That is very irresponsible, and could lead to unwanted pregnancy.
She was a stripper and I was angry at her for not taking care of our baby.
If you girlfriend is working as a stripper to support herself, then that doesn't give you permission to treat her any differently.  Even if she is having trouble taking care of her child, attempting to impregnate her again would only cause more problems.  Like you said, she doesn't deserve this, so you should be more considerate of her from now on.