Do you or your spouse have good friends of the opposite ?

I guess what I am asking really is, do you have friends of the opposite that your spouse is not friends with? And if so, what do you do with this friend as far as keeping a friendship with them going? Do you talk on the phone or e-mail/text? Visit and or go out and do things with them, without your spouse? I know that times have changed, and everyone is allowed to have friends, and it shouldn't matter I guess what they are. People can be friends with the opposite and keep it strictly platonic, but, I was raised very old fashioned and I have a very hard time with having friends of the opposite that my husband is not also friends with, and even if we are both friends with them, I would not be so bold as to carry on conversations via e-mail/text, or to sit and visit with them without my husband, or to go out and do things with them without my husband. That just doesn't seem right to me. And I feel the same if my husband were to do that sort of thing with our female friends, or with his female friends that I am not acquainted with..I am not saying that we shouldn't have our own friends, and we do, and I am not saying that we don't each have friends of the opposite , but what I am saying is, that I don't go out of my way to really converse or have an active social life as far as my male friends are concerned because I feel that would be wrong. What are your thoughts? And, i your spouse had a problem with you hanging out with or spending a lot of time talking to your friends of the opposite sex would you stop out of respect? or would you continue because you don't want anyone telling you who you can be friends with and who you cannot? Just wanna see what the majority says about this. My sis and her hubby is having a problem with this, and I am not sure what I advice to give. By the way, her hubby is the one who wants to be really social with his female friends, friends my sister really doesn't know too much, and she is not liking it at all. And he keeps saying she's jealous and it's silly because he is allowed to have friends. And, one of his friends that he has just really started getting to know is a just turned 18 year old girl. So, what do you guys think? Should my sis have a right to be upset, and should he respect how she feels and not socialize with his female friends without my sister?