The worst thing about marriage troubles is watching the effect they have on our children. Nevertheless, all marriages have to go through them if they are to evolve into healthy ones after the initial years of being-in-love have come to their inevitable end.
You wonder where this will end--try to reassure yourself that it will end in the best possible place: you will be confident, able to deal with any crisis, you will know your deepest needs and how to satisfy them, you will be an excellent communicator, and you will have learned compassion and understanding. Moreover, the better role model your daughter sees you becoming, the more she will follow. Then try to reject any "cheeseless tunnels" which take your energy in less useful directions.
Angel, this time is so difficult, both mentally and physically. For your sake and your daughter's, be kind to yourself and remember that you are undertaking a long journey: try not to expect to much from yourself too soon.
Does your D have a therapist or school counsellor she could talk to for some outside help? I think it might benefit her to be able to express her concerns to someone who is not actually in the situation.
