Help please ? :( is there something wrong ?

me and my gf have been dating for 3 months, everything was perfect, and one night i decided to start an argument because i was mad at a guy, and she thought i was trying to tell her what to do, since the beginning, she didnt get along with her ex/babydaddy, and for some reason i now feel like option, sure they don't talk that much, but they went for a bite to eat 2 times with their son, and he picks her up from work and drops her off at home, one day we got in an argument, she told me that when me and her fight, it makes her miss her ex more, and that kind of hurt, when i explained how i feel, she got mad, shes saying she does not want him, and that if i dont believe her, it's a shame, she hardly ever gets along with her ex, and she says when they do, it's nice, and feels like she has her (crazy) family, and then with me and her, the family she wants . what am i worrying about?