I have a good friend that has been with his girlfriend for a little under a year, and she has 3 little girls. This man adores these girls. He's been supplying them with anything they need and everything they need including a home and food and a father figure. He's no longer happy in his relationship with his girlfriend and is worried that he'll never get to see the girls again. Is there anything he can do to be sure he'll get to see them?

No, unless the mom just lets him, he will have no legal right to visit them

Agree, so he is providing a home for the GF and 3 kids, is that with him? He could just step up to the plate, bite his lip and live life. You are not always going to be happy in a relationship. Pray for most of the time and happy if you get much of the time.