were having과 having 중 어떤 게 맞나요? 관계대명사절도 궁금해요

My friends and I were having/having a great party at the Sunshine Hotel until we met my ex-boyfriend with an extremely attractive woman.
둘 중 어떤 표현이 맞나요? 쉬운 문장 같은데 헷갈리네요 ㅠㅠ