I agree with some of the other responses. When a 12 year old has a boyfriend, they don't mean the same thing that a 30 year old does. While this is true, please don't minimize her feelings. She may feel very strongly about a crush, and you risk putting her down by saying it dooesn't mean anything.
I would stay involved. This is true for friends as well as boyfriends. I had a boyfriend throughout high school, and my parents knew his parents, my friends, and my friends' parents. If I said I went to a friend's house, they asked me when and with who. I never lied and I never had a curfew because my parents trusted me. They realized that they couldn't control every aspect of my life, and discussions focused around making good choices. When a child realizes that their parent respects them, they will strive to make them proud.
My parents only told me they were "disappointed in me" one time in my whole life (I was in my 20s), and I will never forget it. I didn't happen to agree with them, but hearing that from them was devastating.
You should feel lucky that your daughter discusses these things with you. As you said, many kids do not. I think with middle schoolers the more you try to force them in one direction, the faster they will run in the other direction. This is when they start to develop a sense of individuality, and it's our job as parents to nurture and encourage that, rather than feel threatened by it.
Middle schoolers are tough, though. Good luck!