Friends in Marriage

If you’re married/serious relationship is it okay to have opposite sex friends? I have several male friends, 3 or 4, that I went through nursing school with. My SO says I can no longer speak to them because it’s immature to have friends of the opposite sex when you’re in a serious relationship. Am I in the wrong for having these friends? He stopped talking to his female friends, supposedly. Even though I didn’t ask him to because it doesn’t bother me. Thoughts and opinions please.