It is not clear what he wants in terms of changing your mind. Change re: what? Your being with other people besides him or his being with multiple men at the same time?

There is a great Czech book, "The Unbearable Lightness of Being", and a great movie with the same title. Both are a must for you guys, both for content and just because it is great literature/film that you will enjoy. I won't post any spoilers - just read/see for yourselves.