I personally think there is only one question that matters here: do you want this child? If you feel a child would just be a burden to you then, please, please have the abortion. Don't let your son be nothing more than the afterthought of a broken relationship!
If, on the other hand, you absolutely want to be the loving mother who welcomes her child into this world no matter what, then let nothing stand in your way.
That's what I think.