Boyfriend

So my boyfriend has a 10 year old and first of all he didn't know he had this son until his son was 6 years old. When he found out (before I met him) he got to see his son only once in a while because the mother is a nut and she would let him see his son sometimes and then rip him out of his life suddenly. the mother is like 15 years older than by boyfriend too. She has her own man now and it's then and the son.  Well she's starting to let the son into his life again, this is the first time she's allowing this since I've been with him a year and a half. I haven't met his son yet since it's only been a few weeks, he said I can meet him next week. But I live with my boyfriend so when he has his son on the weekends I have to leave cause he doesn't want his son to know I live with him. Ok...whatever, but my issue is the mother. She supposedly hated my boyfriend and wanted nothing to do with him and that's why she kept his son from him, but ever since they started talking again a month ago, I thought it was talk about the son. But I find in his phone messages from her saying her man isn't home, come over and I will leave you trembling, etc going into explicit detail of what she wants to do with him. She calls him nonstop. If he doesn't answer, she keeps calling and freaks out. She's literally crazy. As his girlfriend, I have the right to be upset about this, right? I already feel that she has an advantage over me since she is the mother of his kid. And to see those messages on his phone and to know he lied to me saying he went to meet his son but he really met with her alone (I found the messages from her the next day) I was so upset. And at first he understood and explained to me he would never be with her, it's about seeing his son. But when I could see his messages she would say "why can't I text you? Are you hiding something from me?" So he told her she can't text him since I would see. Now I can only see if I sneak his phone, and I see all the explicit messages. He doesn't retaliate, but I'm so fed up and nervous about it. Especially since he's cheated before. I know nothing happened the night they met, cause I heard her message saying "why did you turn me down, you've never done that before no matter who you were in a relationship with, is it because of your new girlfriend(me)?" So that made me feel better but when I started getting fed up with her messaging him all that and calling nonstop and him always going for a drive to talk to her, never talking in front of me, I get upset and now he's like you know what I don't need to deal with your BS too, it's bad enough I have to deal with her crazy ass I don't need to hear your BS on top of it!!! And now he wants nothing to do with me. I'm so upset and confused I didn't do anything wrong, it's only natural to get upset when you see this woman messaging and calling him nonstop and sending dirty messages telling him to leave me and come over and do things and sending pics of herself saying "tell me I'm pretty!" I know he's annoyed by it too so me nagging him doesn't help. I've stopped now but I'm still upset and he's still sick of me. ?