Can We Still Be Friends?

So, the other day I had a very interesting conversation with a group of my girl and guy friends.  The conversation stemmed from Steve Harvey's first book "Act Like  a Lady, Think Like A Man.  We covered many different topics in the book, then we kinda went into things not concerning the book, just concerning relationships in general.  We got on the subject of  whether or not you can be friends with an ex, and whether or not males and females can just be friends. Obviously there are any number of places that conversation can go, and it went many places. As I've told you all before, I'm still friends with a lot of my exes.  This is mainly because we were friends before we decided to be anything else, and I've never had a bad break-up.  For whatever reasons we decide to go our separate ways, but it's never because something traumatic happened in the relationship. Sometimes, things just don't work out, and you realize you're better off as friends.  A lot of people believe you can't go back to being just friends. I do not agree with that opinion because I'm living proof that it can happen.
Anyway, I mentioned I had a two hour conversation a few nights before with my ex who now has a girlfriend. We don't talk very often, maybe once every other month just to catch up.  Everyone in the room had a fit!  The general responses was: "There's no reason he should be talking to any other woman that long." The consensus was, when you have a mate, your interactions with the opposite sex should never exceed more than a few minutes. (I'm exaggerating, but not as much as you may think)  That whole part of the conversation has been on my mind for days. (rambling from this point on)  Is it time that we start to do some things differently in relationships?  Why is it that we feel like we HAVE to be everything to our mate?  Why are we not willing to accept that there were people in his or her life before we came along and those relationships shouldn't totally end just because we're in the picture? Is it so wrong that he or she may be able to have random conversations with someone who isn't you? I constantly hear "he should be able to talk to me about everything." Look, let's not act like when you date or marry someone, you connect 100% on every level. Surely your mate has interests in things that you have no interests in, and that's fine.  Should he/she not be able to talk about these things with someone of the opposite sex?  Are we putting each other in positions to have to be dishonest?  Another thing I hear when I bring that up is, "you can't leave the door open, temptation is there and blah blah blah"  At the end of the day, we all have a choice.  If I don't really have a problem with my mate having a platonic relationship with a woman and he decides to leave me for her or whatever, that's on him.  I'm not going to absolve him of responsibility just because I said it's okay for them to still be friends and maintain a relationship.  He still had a choice to make. We all have choices, even in the most disadvantageous situations, there's still a choice to be made.  I guess what it boils down to for me, is trust.  I hope I have enough trust in my mate that when he says "she's a friend" I believe him.
I'm going to have to find a long term mate who is as unconventional as I am.  I'm willing to write my own rules in a relationship. I've always been that way. I think a lot of people only see black and white, but there's a lot of gray in this world and you have to be open to doing things that other people might give you the side eye about. Then again, should it matter what your friends think?  Who are you trying to please in your relationship? You and your partner, or the masses?