Hypocritical and immature sound so harsh. Perhaps they are accurate. Tell it like it is and all that?

Perhaps you and your partner might consider investing more in the two of you ... your relationship. It's great to have friends but my partner is my priority. Unless you are naturally up all night, the friend-texting "all hours of the night" sounds like the relationship is regularly on the back burner or there is a passive-aggressive competition going on.

If a friend texts me in the middle of the night and I'm not already awake, I typically don't reply until I'm fully awake the next day. Granted we are in the same timezone. If she was in crisis, I certainly would make an exception.

Your partner's sex chat partner turned platonic friend doesn't sound right to me. I have no advice on how or if you that is something to address. I've purposely not maintained contacts with men I have been in a relationship with even if we broke up on good terms and they want a platonic friendship. I think that is why I question your partner's friendship. Just my two cents. Ignore if it isn't helpful to you. xo