Hey katea, please don't leave entirely.
I totally appreciate that your thread did turn pretty judgemental quite quickly and that is sad. Unfortunately, on an open forum, people don't always ask clarification questions, so they take you at your word in your OP.
You sound like you're going through a tough time and are being pretty hard on yourself already.
Communications between mid to late teens and their parents are not always clear and open; more to the point, a lot of parents think it's going ok and it only emerges much later that things were not as they seemed.
Relationships are hard work and you shouldn't be so hard on yourself; you've dealt with things as you thought fit and (probably) slid into a pattern with your DD which you've just been jolted out of with this 'living together' revelation.
Agree with all the PPs in that, she is old enough to make her own mistakes. Just relax, let her go and let her know that you are always there for her, without judgement (often send messages to my guys when they seem down to just say 'I'm here if you want to talk and I promise to just listen').
She isn't necessarily ashamed of you or of him. It's possible she is simply aware of the disconnect between you (as parents) and him (her peer and BF) and is unable to connect the two worlds; it's not that unusual.
There are plenty of people here who will listen to you, hear you and support you. I remain certain, that is the actual intention of the vast majority of MNetters...
Be strong, and be kind to yourself.