I agree with the concerns everyone is stating here. It does sound a lot like she is in an MLC type situation. IT could also be that she is pushing harder and harder to get a rise out of you, to see how much you care for her, how much it will take to get you to show some jealousy and possessiveness. I wonder if she didn’t come home until late because as she was having a good time and the thought crossed her mind on whether to call or not, she just rationalized it away by thinking Choc won’t care anyway, so what’s the purpose in calling? Your non-reaction when she got home pretty well confirmed that, IMO. I think she could see that she now has an open license to stay out as late as she wants, whenever she wants. You are shooting yourself in the foot by your passivity.
One important way to look at this is to ask yourself how she would react if you did the same. Would she get upset? Would she confront you? Or would she just avoid it as you have? Your calling when you stay out later than expected is you answering to her, asking “permission” in a way, giving her authority to control the M, you abdicating control. So she runs with this power, and you get mad when she doesn’t return the favor. Why should she? What does she have to fear? Why should she not push for more? She just might get it. You will let her have it.
IMO, this has little to do with her. This has more to do with you and you stating and holding to firm boundaries. She cannot push you if you don’t let her. I also suspect she wants you to do this. How else is she to know that you care for her? Words are just words. Stand up and take some action. Show some jealousy. Let her know how you feel. Ask her flat out if she is chasing younger men. Throw something outlandish in her face to make her step back and take notice of her behavior. Make her think twice and become a little hesitant before she acts so that she feels she should come to you for “permission.”