J.D.
i would say that the predicament she's in now is caused by not having a solid long term plan - having a baby with someone she's not married to ensured that there was not even the pretense of permanence in her/the baby's life. giving her a way to escape the predicament she herself (and boyfriend) created lets her continue in the immature fashion that caused the current problem she's facing.
i'd offer her support, but allowing her to make a mess of your life because hers is a mess wouldn't be the most sensible thing for you to do. one day she will have to grow up and realize that the decisions she makes affect her life (and her child's) but they are HER decisions that caused HER problems. SHE'S in control.
on a second note - i pray that you and your boyfriend will give your child the stability and permanence that marriage would bring. bless him for treating your son well, but imagine the heartache your son would suffer if this second father figure were to leave.. God would look favorably on both of you!
God bless