See, going to movies with the opposite sex is a little bit unorthodox in my opinion if you have a partner. You can arrange to take along your partner as well though. But going to lunch is all right IMO.

It is all right to have friends from the opposite sex, but you should be more thoughtful of your partner's feelings. Going out to movies with someone from the opposite sex other than your partner and just the two of you doesn't sound right to me.