I think when you really care about the next person, you can compromise on stuff for them. If she really loves you she should be ready to give up on her male friends for you. That is if you're also willing to do the same for her. If this thing bothers too much and she's adamant on being with her friends, I don't see why you should put up with it. Talk to her and then make a decision. If you stay together you can't help being bitter about this and that would affect your relationship negatively, and hurt you both in the process.
Leave her, but stay friends. Loyalty is one of the best qualities that a woman can have. She sounds like she will be trouble in the future and a huge headache. Imagine being committed to her, being in love, and having children with this woman and it's Friday evening and she is off to hang out with "Dante" or "Andrew" or "Ramon" (yeah Ramon is the Spanish guy who also takes her to dance tango then he gives her a massage after to help relax her muscles). See what I mean this will only get worse. There are so many women out there who will not play this manipulation game (which is what she is doing). There is a loyal woman out there who is just as attractive and fun as this one but who won't mind f*&% you. I was a young man once and the older you get the less BS you want to deal with. Cut and run. Find someone who has the same loyal point of view and is more fun.
You need to understand this. when you love someone you ought also to free that person. If you go on like this you will be encouraging her to do it the more. You can not overcome something wrong with a wrong motive but with a good motive. Just be good and appreciate and give her a smile when she tells you about what has happened. Remember you don't own her fully until she becomes your dear wife. So do it with love. Talk to her even when she is out there with them always mentioning this that you love her.
Let her go!
Dump her if she knows it hurts you and she still does it then she don't care about you
Is it a business appointment. Learn to trust her if it is about business but it is much okay if you will accompany her.