Why Won’t She Change Her Surname

I need to know if I am in the wrong here, I am pretty sure I am not.

My partner was married for 11 years to the mother of his three children, I met him 2 years after they had split and we are very happy together and I get on really well with his three children there is only one problem, my partners ex-wife!!!

She kept his surname when they split and I didn’t say anything straight away I then asked him why she still had it when they are divorced, he did not answer me.

Since then she has remarried changed her name to her new married name divorced again and gone back to my partners surname.

Am I wrong in asking him to ask her to go to her maiden name and not his name?? We are going through a bad patch on the verge of splitting up as it is. I have to deal with her going to his family parties which I hate and now she has gone back to his name.

We were planning to get married in the next few years but I refuse while she has his name. Surely when u divorce u would go back to your maiden name.

He argues that she may want the same surname as their children but this argument is invalid as surely she would have kept that name when she married her last husband, i cannot share the same name as her, especially as she is still unfortunately very much part of our lives.

Everyone I have spoken to says that it is strange or one person commented that her maiden name must be awful to avoid using it again (it’s a pretty normal surname) am I wrong to feel upset and annoyed by this or am I being selfish or unnecessarily annoyed?