fiancé seeking ex help...

my fiancé takes medication for his epilepsy and he changed insurance and the new insurance asks for a deductible of $280 to buy the medicine ... we didn't have the money so he asked his daughter's mom to borrow the money... makes me feel bad that I couldn't help him now i feel totally worthless and jealous. she said "oh your girlfriend doesn't have the money?" like i saw the messages and he didn't even say anything she talks a lot of shit about me and he doesn't even bother to tell her to shut up because he is scared she may take the little girl away from him . I understand but it's been a year and a half and i been dealing with her putting me down like that she doesn't want to meet me ever since i meet my SO. so many stuff going on I won't even end. the point is idk what to tell my fiancé i am tired of putting all this stress on my baby because she OBVIOUSLY stresses me SO DOES MY FIANCE. i am a bigger person this is why I've never say anything to her. she is like 5 years older than me and I've seen how crazy she gets when she is mad.