Should I Allow my Husband's Ex to Stay with us

My husband claims to still be friends with his ex who he was engaged to for 3 years, he asked me two nights ago if it was okay for her to come stay at our place for 3 weeks because she is coming to the UK for vacation but does not know anyone...
Hello....... so why is she coming?

I told him NO WAY!and now he is not talking to me, please what is my offence ?