Am in the wrong or right ?

So yesterday my husband went to his friends house , where his ex lover also lives . His friend and the lover are related they are cousins . So I am upset because he went and I stayed home and he took my son which I let my son go because he wanted to go . Am I in the wrong feeling upset for him going to his ex lovers house ? He didn’t offer to take me with him so I felt like ok ?? We have gone to places where she has been there . So the friend said she’s wasn’t going to be there supposedly but he always says that , and come on she lives there so of course she would be . So I want opinions because he says I’m in the wrong for being angry at him . Because he said if she was there he would come home . I feel disrespected because I would never even consider going to my lovers house . I’m sure he wouldn’t want me going to the house of the man I cheated on him with . Sorry it got long . So should he have gone ? Should he have respected the fact that ok no my ex lover lives there so no I’m not going . Also his friend knows everything that went on and he doesn’t care at all. He says I’m over exaggerating and I have no right to be mad that it was just a birthday party and his excuse for it being ok is that my son went with him that he wasn’t going to do nothing. He just said oh I’m going to his house ok , he didn’t say is it ok or anything like that he just made his choice and choose to go . I saw that she sat across from him at the party only because someone I know told me that . I just feel it’s a disrespect to go party to an ex lover who you were planning to move in with and leave your family for . We decided to work things out and then this happens .

Also no I wasn’t Invited