Ugh, she sounds like a dictator and quite envious. I would start separating from her. You're in a Vee, she is not your lover and you don't owe her anything more than polite acknowledgement. Respect for each other should be sufficient. You don't need to tell her jack shit if you don't want to. Do not share what you do not want to share, and do not get involved more than you want to. Egad, the things that people demand! And put up with! Take a stand for your own personal boundaries, for goodness sakes, and ask her to honor the relationship you have with the person you are involved with. Jeez.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein