Boyfriends Baby Momma is Crazy?

So let me rephrase the way i asked the quetion before. Me and my boyfriend have been together for over 2 years and everything is great between us. The only problem is that he has a three year old son that he has just started seeing a year ago ( thanks to my pushing him). Before you get any mean thoughts and write negative things about my boyfriend let me break it down really quick. He was with his ex for 4 years and well he was very tired of dealing with their relationship together (she was actually crazy, I mean really really crazy no joke) so they broke up. Well later she comes back saying she was pregnant and he felt like crap, so they stayed together...(surprise she really wasn't preganant; however she made sure to get pregnant this time around. So anywasy he broke up with her again and then when she was delivering the baby he went to visit her in the hospital and she sent him away, saying the baby wasn't his. So whatever things went on in between, the about 1 1/2 years ago we see a pix of her and the baby on her myspace and the baby looks like his twin. Well now he's been seeing his son for a year now, but this girl wants to be with him again. she writes all over her myspace about how she loves him and she writes to me saying he's going to leave me for her. Blah blah, the typical thing. So my thing is, he isn't on the birth certificate at all so i know he doesn't have rights; however where does he go to get things going to get legal rights to his son. She drives me nuts, no matter how much i try to ignore it, i cant help but fall into her trap and talk **** back.