I Need Some Advice

I am a young women in a committed relationship. Everything is quite good. Except for the fact the he has a baby. It is not the baby that is the problem, it's the baby's mommy. She will barely ever let my boyfriend see his own baby girl. But, she expects him to pay for diapers, clothes and all that stuff. This wouldn't be a huge problem if she actually let him be a part of the child's life. Also, let me tell you that when this baby was conceived, my boyfriend was only 16 while this girl was 19. She chose a kid [at the time] to be her sperm donor.  I want the best for my boyfriend and his life because we are hopefully spending the wrest of it together, or at least for along time to come. This is hard for him to handle and I am the one beside him. I am here through it all,but this puts me through emotional strain also. All in all,this girl is stealing my boyfriend's life away by taking is child and is now trying to get money from him [which he doesn't have] because he is 18 now. I would just like some advice on how to handle all of this and how to help him.