How do you deal with...(long)

Crazy women who have no respect for your relationship and text your boyfriend dirty things knowing he has a girlfriend?! Especially if it's the same woman over and over again who doesn't get the hint and says "well i don't need a relationship w/ you, I just want to f**k you...if you don't answer me then you must be with 'her' " basically saying I don't care you have a girlfriend. And if this woman happens to be the mother of his kid.. Never had a relationship and didn't even know he had the kid til the kid was 6, he's now 11. But this woman is obviously never going away and she will not give it up. Idk what to do. She tells her son that I'm evil and that his dad is going to choose me over him and care more about his girlfriend than his own son so his son doesn't want to be around me now, and that means I have to leave the house when he has his son. And he kisses her ass because the kid listens to her every word so if she says anything bad then the kid won't want to see him anymore. Regardless of the fact that he pays child support and he's been to court and they said he can have him every other weekend. I feel like I have to share him with this woman. For the rest of my life and I just don't know how to deal With this. Maybe it's because I'm 21 and he's in his 30s so it's not something I'm used to. But if the situation was normal I think I could get used to it. I just can't help but feel jealous over this woman. Not until I have my own child with my boyfriend. I feel like then she wouldn't have such an advantage over me. Because although he's never getting back with her,  as much as she comes into him, (she's like 48 and gross too) she's still the mother of his child.